Hydrometallurgy 133 (2013) 23–32Contents lists available at SciVerse ScienceDirect Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet Review Hydrometallurgical recovery/recycling of platinum by the leaching of spent catalysts: A review Manis Kumar Jha a, Jae-chun Lee b,⁎, Min-seuk Kim b, Jinki Jeong b, Byung-Su Kim b, Vinay Kumar a a b Metal Extraction and Forming Division, National Metallurgical Laboratory, Jamshedpur-831007, India Mineral Resources Research Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, Republic of Korea a r t i c l e i n f o Article history: Received 17 April 2012 Received in revised form 3 November 2012 Accepted 22 November 2012 Available online 28 November 2012 Keywords: Spent catalyst Platinum Leaching Recycling Hydrometallurgy a b s t r a c t Platinum is one of the precious metals with many applications, including in catalysis, electronic devices and jewelry. However, its limited resources are becoming depleted. To meet the future demand and conserve resources, it is necessary to process spent platinum-containing materials, such as catalysts, electronic scraps and used equipment. These materials are usually processed by pyro/hydrometallurgical processes consisting of thermal treatment followed by leaching, precipitation or solvent extraction. This paper reviews platinum leaching from such resources using acidic and alkaline solutions in the presence of oxidizing agents, such as nitric acid and hydrogen peroxide, sodium cyanide and iodide solutions. The results of the study are described with respect to the recovery of platinum and other metals under the optimized conditions of leaching with lixiviants. Previous studies have achieved platinum recovery using aqua regia and acidic solution in the presence of chlorine to produce platinum from spent catalysts on a commercial scale; however, the process generates toxic nitrogen oxide and chlorine gases. This paper reports the salient findings of efforts to replace the aqua regia with hydrogen peroxide in acidic solution, chloride salts, sodium cyanide and iodide solution to improve the economics of the existing processes and reduce the environmental pollution. © 2012 Elsevier B.V. All rights reserved. Contents 1. 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . Processing of spent materials . . . . . . . . . . . . . . . . . . . 2.1. Thermal pre-treatment of materials . . . . . . . . . . . . 2.2. Hydrometallurgical processing . . . . . . . . . . . . . . . 3. Leaching of materials . . . . . . . . . . . . . . . . . . . . . . 3.1. Leaching in aqua regia solutions . . . . . . . . . . . . . . 3.1.1. Leaching in aqua regia and after pretreatment . . . 3.1.2. Leaching with aqua regia after acid/alkali treatment 3.2. Leaching in the presence of chloride ions . . . . . . . . . . 3.3. Leaching in the presence of hydrogen peroxide . . . . . . . 3.4. Leaching in cyanide solution . . . . . . . . . . . . . . . . 3.5. Leaching with iodide/iodine solution . . . . . . . . . . . . 4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Introduction Platinum (Pt) is a costly precious metal with applications in the manufacturing of catalysts, electronic devices, space materials, biomedical ⁎ Corresponding author. Fax: +82 42 868 3415. E-mail address:
[email protected] (J. Lee). 0304-386X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.hydromet.2012.11.012 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 24 24 25 25 26 26 27 28 28 29 30 30 30 30 devices and jewelry, among others, due to its chemical resistivity, high-temperature stability and stable electrical properties. The natural resources of platinum and platinum group metals (PGMs; platinum, palladium, rhodium, ruthenium, iridium and osmium) are limited and mainly found in Russia, North America, Canada and South Africa. South Africa is the world's largest producer of platinum, which is mined in an area called the Bushveld Igneous Complex. The PGM concentration is which are considered environmentally hazardous waste due to the presence of various ionic constituents.. 5 h) to eliminate coke and water. Germany. producing a mass loss of 6–8 wt. the PGMs present in the ore as their sulfides. such as organometallic catalysts from chemical and petrochemical industries. At the Umicore precious metals refining plant. 2006). The details of the processes are not available in the literature. Platinum group metals are employed as the active species for catalysts. converter-recycling. 2011). 2000). The composition of some spent catalysts is shown in Table 1.. Williams et al.1. 1 atm.. 2011) • Spent Pt–Rh or Pt–Pd–Rh alloys: Catalytic oxidation of ammonia to nitrogen oxide by air (Mahmoud. A number of platinum-based catalysts are available and applicable for various purposes. Thermal pre-treatment of materials Thermal pre-treatment is employed during the processing of different spent materials. respectively. The global Pt demand increased by 16. This process will conserve the resources to meet the future demand for Pt and other PGMs and also reduce environmental pollution. by SX. such as sulfur. and no losses of other elements were observed.. chemical leaching and refining to recover Pt. Matjie et al. depending on the presence of other constituents. electronic scraps. 1971) • Pt–Zn–Hy catalyst: Hydro-isomerisation of n-heptane (Saberi et al. 2001) • Pt-alumina catalyst promoted by Fe-oxide: Oxidation of CO in H2 (Liu et al. USA. The Pt demand is increasing worldwide due to its versatile applications in various industries. 2004) • Pt–Sn–In/Al2O3–Li catalyst: n-Paraffin dehydrogenation to produce alpha-olefins (Pinheiro et al. nitrogen or air..com/p02/USWeb-Internet/converter-recycling/ en_GB/. 1971. The classical chemical approach for Pt recovery from ore has been documented by Gouldsmith and Wilson (1963).. 1982) • Pt–cobalt based catalyst: Fischer–Tropsch (FT) process to produce hydrocarbons from synthesis gas (Matjie et al.. such as Au. Belgium. The concentrate is then leached in aqua regia to produce a leach solution containing Pt and other precious metals. respectively. The spent materials are segregated. The carbon and iron were quantitatively removed as CO2 and Fe2O3 dust. Gates et al. Pd. Ag. Pd and Rh. The deactivated catalysts are discarded or sometimes regenerated in situ or replaced by fresh catalyst. it is necessary to process secondary materials.. The fused mass was dissolved in water. 1992.0% in 2010 and 2011.. poisoning and/or thermal degradation/sintering (Bartholomew et al.% (Pinheiro et al. depending on the undesired organic constituents to be removed to produce ash containing PGMs (Aberasturi et al. crushed. . UK employed smelting. 2003) • Pt gauze catalyst: Oxidation of ammonia to produce nitric acid (Barakat and Mahmoud. and the cost of production has been increasing due to the decreasing PGMs concentration in the remaining naturally occurring ore. including Pt. thus. UK. (2005) reported the removal of wax from spent catalysts by calcination at 800 °C before metal recovery by leaching. Pt is employed as a catalyst in various chemical reactions. Nippon/Mitsubishi. 2004) and aromatic nitro compounds reduction (Ghosh et al.g. 2004) • Bimetallic Pt–Cu catalyst: Nitrate reduction (Epron et al. Thermal degradation is induced by thermal shocks due to heating and cooling during operation. 2002) • Pt and Ni catalyst: Acetophenone hydrogenation (Malyala et al..basf. Therefore. by different corporations and industries (e. Processing of spent materials Spent catalysts containing Pt and other ingredients are processed to recover and recycle metals. Umicore. The metals from the leach solution are separated by precipitation or solvent extraction (SX). Twig. fabricated ware and membrane electrode assemblies. in the range of 2–10 ppm (g/t). arsenides or tellurides are concentrated by physical beneficiation followed by pyro/hydrometallurgical processes (Seymour and O'Farrelly. as follows: • Pt–Pd–Rh auto catalyst: Reduction of toxic gases of automobile (Aberasturi et al. Johnson Matthey. 2000).. USA and Johnson Matthey. 2002) • Pt–C catalyst: Hydroxylamine sulfate manufacturing (Grzelczuk et al. Pd. 2004) • Pt/Rh bimetallic catalyst: Catalytic reforming to upgrade the low octane naphtha to higher octane aromatic hydrocarbons (Kluksdhal. such as hydrogen. 2005) • Pt–Al2O3 catalyst: Catalytic reforming (Pinheiro et al.K. 1987. http://www. which improved metal recovery during leaching due to the elimination of the hydrocarbons and charcoal present on the catalyst surface and reduction of oxidized PGMs (Bolinski and Distin. 2005) have treated Pt/Rh bimetallic catalysts using microwave heating before leaching in aqua regia. To recover Pt. 2004). Cramer (2001) reviewed the processes for the production of Pt from South Africa's PGM ore concentrate following pressure leaching in HCl solution and the separation of PGM. 2010).0% and 19. 1985) • Pt-base metals catalyst: Reforming and isomerization catalyst (Jeliyaskova et al. The selection of processing steps depends on the metallic constituents and other associated materials. 2004).24 M. Rh) were heated under a hydrogen atmosphere at 250 °C. which is further processed by hydrometallurgical route to recover the metals (Hageluken. 1983. The precious metals on automotive catalysts or spent materials are chlorinated with chlorides at an elevated temperature to vaporize these metals (Shoji. 1982. The results of studies available in literature are mentioned below. / Hydrometallurgy 133 (2013) 23–32 low. BASF/Engelhard. and poisoning occurs because of strong chemical bonds between a feed component. Dowden. oxygen. Spent Pt-based commercial catalysts (Pt and Pt–Sn–In/Al2O3) were fused with KHSO4 at 450 °C for 3 h to recover Pt and other metals (Junior and Afonso... Some authors (Jafarifar et al. The deposition of coke is the most common form of catalyst fouling. 1997. used equipment. Jha et al. for Pt recovery and recycling. Japan). spent catalysts are an important secondary source for recovering Pt and other associated metals. The precipitate is then calcined to produce Pt sponge. 1990). McCoy and Munk.. Other metals present in PGMs are recovered by further processing the solutions. 1980. To recover the metals from different spent materials. 2. or catalytic reaction products with active sites on the catalyst surface.. The depletion rate of high-grade PGMs resources has been increasing due to increasing demand. BASF. The Pt is precipitated as ammonium hexachloroplatinate (IV) [(NH4)2PtCl6] with NH4Cl from the purified solution. 1989). spent catalysts and e-wastes are smelted in a furnace to produce a concentrate containing Cu. Pt and other metals. Chlorine and carbon monoxide are also employed at high temperature to produce Pt carbonyl chloride [Pt(CO)Cl2] vapor for metal recovery (Kim and Woo. 1979. Hereaus. which is further treated to produce pure Pt metal. 2. The catalyst samples (Pt/Al2O3 and Pt–Sn/Al2O3) were heated under oxidizing conditions in a furnace under air (400 °C. The materials are thermally pretreated in a suitable environmentally friendly atmosphere. Pt was recovered as a waterinsoluble residue and tin and indium as sulfides at pH 1. 2006). in comparison to 2009 (Matthey. pyro/hydrometallurgical processes are usually employed for the effective extraction and separation of metals. PGMs are recovered as a byproduct or coproduct depending on their concentration in the ore.php?pagename=Theprocess). and generally associated with base metal sulfide minerals.. Rh and other associated metals (http://www.. such as spent catalysts.. Catalyst deactivation: Catalysts are deactivated during use due to fouling. 1998). ground and then processed by pyro/ hydrometallurgical processes to recover the PGMs. steam reforming of n-butane to produce hydrogen (Avci et al. Trimm.. 2011). to improve the leaching efficiency for metal recovery.jmrefining. Spent automotive catalysts containing PGMs (Pt.com/page-view. Belgium. bromine. The process is energy intensive and generates atmospheric pollution due to the evolution of toxic gases.5 mm) which is ground to 200 mesh powder by porcelain ball mill.30S. iodine. 0. 1984. However. 1.5 C. Pd. 1986). time. 2011. including Pt. Ezawa. 1993.15 Ca. 1989. The powder was dried (by heating 120 °C for 24 h) before dissolution experiments.2. 1983. The catalyst supports. 2009). Keyworth..05 Zn. in all the cases the total content of PGMs is always lower than 0. Yoo.46 Ni.05 Fe. 0. etc. Ryder and Dymock. Pd and Rh from spent automotive catalysts and described the problems faced due to the presence of other metallic constituents. Catalytic oxidation of ammonia to nitrogen oxide by air contains 16. mainly oxides of Ce. The PGMs Pt. Catalyst composition Composition and other details Reference Spent Pt–NiO/ γ-Al2O3 Spent Pt gauze catalyst Spent Auto catalyst Nitrogen production unit of petrochemical plant. e. Duyvesteyn et al. 0. were studied for Pt leaching from different spent materials (Kikuchi and Eto. Pt is then recovered as ammonium chloroplatinate with the addition of ammonium chloride. Leaching in aqua regia solutions 3.. 1992. Leaching of materials The leaching of Pt and other metals is usually carried out using different lixiviants. / Hydrometallurgy 133 (2013) 23–32 25 Table 1 Composition and other properties of spent catalyst. Ni.0 C. The smallscale process with 95% Pt and 98% Pd recovery was used for commercial applications. 1996.15 Cu. The oxidizing agents are also added to enhance the leaching efficiency of the metals.14% Pd.37 Pt. 0.37 Pt. 8.24 Re. Mishra and Reddy. 0. 2. 0.%: 0.%) as 13. Pt–Re–Al2O3. temperature. Fe and alkaline-earths (Palacios et al.1%. Precious metals in the melt are separated by allowing them to adsorb on Fe or Cu with high specific gravity. Day. Rh are present on wash coat. 48.% 91.%: 0. Colombo and Bowman (1996) reported a process for recovering Pt from a naphtha reformate spent catalyst using carbon tetrachloride vapor in air or N2 and obtained over 95% Pt recovery. The Pt in the solution is concentrated by evaporation to recover Pt while recycling HCl for leaching. Heraeus. Chemical analysis of powder is (in % w/w wet basis): 0. Wax (60–70%). proceedings and patents (Eugenia et al. 0.. (1985) used oxalic acid to leach out precious metals from bimetallic reforming catalysts.. Han and Meng. 5. 3. La. Canada (Ryder and Dymock. 0. and then heated in a furnace together with ore and scraps to produce concentrated Pt for subsequent recovery. 1997. 2006). (2004) Spent reforming catalysts composition in wt.. Jha et al. (Cuif et al.125 Pt. Pt–Ir–Al2O3. 0. 1990).1.5×6.44 Li. Hoffmann (1988) reviewed processes for the recovery of Pt. The process is catalyzed using Fe or other transition metals.01% Ag and 0. 2007).pdf). Meng and Han. nitric acid.17 Zn. 1. 1994.8 carbonaceous material.26 In. 2. from spent materials using hydrometallurgical processes consisting of leaching in hydrochloric acid under oxidizing conditions followed by selective precipitation and ion exchange (http://www. 1994. In this process. 2000). cobalt oxide (8–10%). 2.K. 0. the leached chloroplatinic acid solution is purified with respect to base metals by precipitation. 1988.M. Mishra. as evident from the various papers appearing in journals. quartz and hematite as the major phases.. 1995. a highly polluting gas generated by the current combustion-based recycling Zanjani and Baghalha (2009) process (Shore. is incinerated to remove non-metallic components. Harjanto et al. BASF Catalysts LLC.0012 Au and major amount of iron oxides and silica. and minor constituents The smelting process is also employed to produce concentrate containing Pt and other metals for subsequent hydrometallurgical processing (Benson et al. 0. such as alumina.30 Al) catalysts Pinheiro et al. Platinum Lake Technology Inc.13TiO2. Kayanuma et al.76% Pt.17 Pb.1. This process has serious environmental effects. Bolinski and Distin. 2001. mullite or cordierite (2MgO·2Al2O3·5SiO2).. 0. hydrogen peroxide. and Pt–Al2O3. to obtain a lowviscosity slag. metal recovery (or recycling) through hydrometallurgical route is important because of its low cost and eco-friendliness in comparison to other recycling processes. 0. Nippon PGM Co. 50. Germany recovered precious metals. concentration and pressure. Zr. Spent catalyst dust collected from a fertilizer plant: (wt. chlorine. Hydrometallurgical processing In hydrometallurgical processing. aluminum oxide (20–27%) and minute amount of platinum Pt/Al2O3 (wt. Leaching in the presence of other chloride ions . 0.28 Zn. USA reported a new process for precious metal recovery from membrane electrode assemblies (MEAs) eliminating the emission of hydrogen fluoride. 0. reported commercial-scale PGM production from different resources (Suzuki et al.g. 1992. The new process consists of grinding the material followed by leaching with HCl/HNO3 to dissolve the Pt in the solution.35 Mg.9 Al2O3. 5 humidity.24 Pt. The spent catalyst is in the form of cylindrical pellets (6..87% Rh.41 Sn. Low-grade scrap from the electronics industry and catalysts. Pt leaching with aqua regia after acid/alkali treatment 3.84 Re.02 Cu. Lucena et al. are melted.com/media/webmedia_local/media/ presse/termine/earthday2010/PreciousMetalsRecycling_technology_ report_02_E.1. among other sources. (2004) reported the recovery of PGMs from scrap by smelting with copper to obtain metals for further processing to dissolve metals in a suitable lixiviant.28C. 3. 2. metals are leached directly or after pretreatment using suitable acidic and alkaline solutions in the presence of oxygen. The results of Pt leaching from different secondary materials are classified and presented below.7 Pt. which was subsequently heated to yield platinum sponge. sodium cyanide. 1999) and ~90% γ-Al2O3 and a mixture of base metals additives. Mishra and Ramadorai (1988) studied the continuous leaching of automotive catalyst in HCl and its regeneration process scheme on the bench scale with PGMs recoveries of 95% Pt and 91% Pd. 0. 1. 3. Many authors have studied Pt recovery from waste catalysts and secondary materials.corporate. 0. such as insulation and plastics. including cobalt and promoted Matjie et al. Fe–Pt–Re–Al2O3 and Fe–Pt–Ir–Al2O3. 0.2. Angelidis and Skouraki (1996) Spent catalysts Pt–Rh or Pt–Pd–Rh alloys Spent Fischer– Tropsch catalyst Pt/Al2O3 Pt–Sn–In/ Al2O3–Li Pt catalyst Barakat and Mahmoud (2004) Aberasturi et al.60 Al) and Pt-Sn/Al2O3 (wt. 0.5 Ni. The most common car catalytic converters are the honeycomb type cordierite skeleton (2MgO·2Al2O3·5SiO2). 2000. 1990) developed a hydrometallurgical process for the recovery of precious metals from spent automotive catalysts following acid leaching in chloride medium. chloride or iodide solutions. 0. The effects of different process parameters. 16. 5. 1998).9 Fe. Chiang et al.2. Leaching in aqua regia and after pretreatment 3. and the lengthy overall flow sheet results in unavoidable PGM losses. 1.1. Narita (1998) investigated a method of recovering Pt from sludge and dust. hydrochloric acid.15 Fe. in some cases with CaO at elevated temperatures. Pd and Rh. McVicker et al.98 LOI...19SiO2. (2005) with minute quantities of group VIII noble metals such as Pt..heraeus. (2011) Mahmoud (2003) Used to produce hydrocarbons from synthesis gas.3 Rh. such as sulfuric acid. (Angelidis.25 Si X-ray diffraction analysis indicated the presence of Pt. These are classified as given below. As Pt forms stable chloro-complexes in chloride solution at high acid concentration. Jeliyaskova Leaching of alumina with et al. Leaching in aqua regia and after pretreatment Different authors have used aqua regia to dissolve Pt and other associated metals in catalysts (Muraki and Mitsui. The rhodium present in the catalyst could be selectively dissolved with sulfuric acid. (2005) aqua regia at liquid to solid ratio 5 and 2. Pt and Pd leached at 95 °C Ammonium hydroxide used to get salts of hexachlorocomplexes which are then reduced with hydrazine hydrate to produce Pt–Rh powder. − þ − NO3 þ 4H þ 3e ↔NO þ 2H2 O ð2Þ 2NOClðgÞ→2NOðgÞ þ Cl2 ðgÞ ð3Þ NOCl þ H2 O↔HNO2 þ HCl ð4Þ − þ 3Pt þ 4NO3 þ 16H →3Pt − þ Pt þ 4NO3 þ 8H →Pt 4þ 4þ 2− Table 2 Leaching in acidic solutions after pre-treatment. Leaching in the presence of hydrogen peroxide 3. The resulting leach solution was filtered at pH 1. The sample was refluxed with Jafarifar et al.4. is suitable for Pt leaching because of its high oxidation potential of 0.1. catalyst HCl–Cl2 Ash of calcined Pt–C Aqua regia spent catalyst. / Hydrometallurgy 133 (2013) 23–32 3.5 h to solubilize Pt.7%.5 h. Perte et al. ð5Þ ð6Þ ð7Þ 3. Aqua regia was used to dissolve Pt at 80 °C in 1 h from the ash obtained after the calcinations of spent Pt–C catalyst from a hydroxylamine sulfate manufacturing plant (Grzelczuk et al. respectively. 97. the ash obtained after (1985) calcinations of Pt–C spent catalyst Pt precipitated as (NH4)2PtCl6 Horner with ammonium chloride and and decomposed at 800–900 °C to McGrath.0% and 92. 1995).7% Pt and 1. The residual Fe powder was separated magnetically and recycled. but the Rh leaching rate is relatively low.0.. Tyson and Bautista (1987) leached Pt and Pd of the spent catalysts within a given particle range (− 60 + 70 mesh to − 120 + 140 mesh) with 3791 ppm Pt and 1306 ppm Pd in a packed bed reactor using different HCl:HNO3 concentration ratios.1.1. SiO2 or carbon Spent catalyst Aqua regia Scrap from glass industry Aqua regia Spent catalysts HCl:HNO3 concentration Aqua regia Barakat and Mahmoud (2004) Bonucci and Parker (1984) Al leached with sulfuric acid Eugenia et followed by Pt with HCl–Cl2 al. sulfuric acid followed by Pt (1982) leaching with aqua regia Pt dissolved in aqua regia. Pt was separated using trioctylamine and recovered by precipitation. which is then treated with ammonium hydroxide to obtain salts of hexachlorocomplexes. The Pt and Pd recoveries were 95.3. Spent catalyst containing 13. HNO3. The leaching extent was 90% and þ þ 6H þ 4NO þ 8H2 O þ 4NO þ 8H2 O þ 4NO2 þ 4H2 O: Spent auto catalyst HCl and HNO3 Pt-alumino-silicate Sulfuric acid.. In the case of metal dissolution with aqua regia.26 M. (Tadashi.0% and 92.K.7%. the formed nascent chlorine (Cl2) and nitrosyl chloride (NOCl) provide high oxidation potential and the high chloride-ion concentration acts as the complexing agent (Burkin. The other associated metals (Pd. 200 ppm Pd and 300 ppm Rh on Al2O3 substrate in aqua regia. Almost of Al. leaving Pt and Pd in the residue. respectively. (2005) Pt and Co species dissolves during NaOH–HNO3–aqua regia leaching. Calcination of precipitate gives high purity Pt (>99. The oxidizing agent.7%.3% Rh was refluxed with aqua regia at an L/S ratio of 7. Pt could be leached at a higher potential using an oxidizing agent (Lide. Muraki and Mitsui (1986) patented a process for recovering Pt and Pd loaded on granular or honeycomb Al2O3.5 for 1. a kinetic expression was determined empirically for the experimental data. SiO2 or carbon support by leaching with aqua regia. and 86. which is washed to produce the high-purity product (98%). Pd and Rh were 99.0. 1999). Material Leaching agent Results Reference Spent reforming catalyst Aqua regia solution Baghalha et al. 1994 obtain Pt black. The reaction rate was initially high but dropped quickly with time for both metals.5. The salient details are summarized in Table 2. respectively.96 V according to reaction (1). Leaching in aqua regia solutions The leaching of a metal is mainly governed by the formation of a complex under the potential and pH of the solution in the presence of ionic species. dissolved from catalyst by H2SO4 followed by Pt recovery (1985) from residue Recoveries of Pt and Pd were Muraki 95.5% Pt recovery was achieved. Perte et al. Tanaka Noble Metal Ind.99%) Recovery of 90% Pt and 70% Pd in 5 h leaching time. (1983) Pt dissolve at 80 °C in 1 h from Grzelczuk et al. 100. 1982) has taken out a patent for the recovery of metals from spent catalysts containing 1000 ppm Pt. Rh. not Matjie et in other lixiviants. The salts are then reduced with hydrazine hydrate to produce Pt–Rh powder. >95% Pt and Rh recovered. 1986). Almost all of the Pt were recovered and recycled to produce Pt–C. al. The material was dissolved in aqua regia and precipitated with NH4Cl. 1985). The recoveries of Pt. and metals from the solution were precipitated with addition of Fe powder. and Mitsui (1986) Schreier and Edtmaier (2003) Tyson and Bautista (1987) . HNO3 and HCl undergo through reactions (2) and (3) (Massucci et al. (2009) Pt gauze dust Aqua regia solution The Pt leaching reaction was controlled by surface chemical reaction and activation energy was found to be 72. Spent Pt gauze Aqua regia Pt/Rh bimetallic reforming catalyst Aqua regia solution Reforming and isomerization catalyst Fischer–Tropsch catalysts Sulfuric acid followed by aqua regia Acidic and alkaline solutions and aqua regia Pt–Re–Al2O3 catalyst Hot sulfuric acid Pt and Pd honeycomb Al2O3. The alumina co-dissolution was reduced by the thermal pre-treatment of the catalyst without affecting Pt solubility. Leaching in cyanide 3. etc.1 kJ/mol. 1988 ð1Þ HNO3 þ 3HCl↔NOCl þ Cl2 þ 2H2 O 3Pt þ 18HCl þ 4HNO3 ↔3½PtCl6 (1988) patented a process for the recovery of Pt along with Rh from spent catalyst using aqua regia leaching. Bonucci and Parker (1984) dissolved Pt along with Pd from the crushed spent automotive catalyst in an agitated reactor in HCl solution using nitric acid as oxidant at 95 °C. Leaching with iodide/iodine solution 3. 2001).) also form chloro-complexes at lower potential and will also be leached. Based on these studies. The solution is then purified by ion exchange to obtain pure solution. McVicker Re and most of Al2O3 are et al. Jha et al.. 17 Zn. respectively. Subsequently.6 Co and 0.17 Pb. 20–27 aluminum oxide.2% Pt. Jeliyaskova et al. .04–0. 1983). Subsequently. high-value cobalt and platinum using different lixiviants. in 5 h. 0. 1.05 Pt) was studied for the selective recovery of alumina. which can react with sodium hydroxide and inorganic acids.%: 8–10 cobalt oxide. The residue is then leached with concentrated HCl and chlorine gas at 95 °C to dissolve Pt (Eugenia et al. The clarified solution was obtained by filtering the slurry for subsequent Pt recovery. In the first method. 2004).1. The recoveries of Pt were 96. A Pt recovery of 97. 2005).2% and 98. small amount Pt. 2 (Matjie et al. The Pt extraction rate was increased significantly by increasing the L/S mass ratio and the reaction temperature. This large value indicates that Pt extraction in aqua regia solution is controlled by surface chemical reactions. respectively. Horner and McGrath (1994) also reported the use of aqua regia to dissolve Pt from spent Pt gauze followed by precipitation as (NH4)2PtCl6 with ammonium chloride and thermal decomposition at 800–900 °C to obtain Pt black (Yoo. 2003).25 M) at pressure ~9 bar and 170 °C during two consecutive leaching steps. respectively.3 Rh. The leaching kinetics followed the power-law rate with an activation energy for the platinum surface dissolution reaction of 72. 1.35 Mg. The calcined catalyst (wt. 0.1 kJ/mol.7 Pt. 1998). McVicker et al. 150 W microwave radiation was used with aqua regia at a liquid/solid ratio of 2 for 5 min.5 in 1.M. 5455 mg/kg Rh and 168 mg/kg Pd) was studied for the recovery of metals using aqua regia (Schreier and Edtmaier. 60–70% wax) was processed to recover Pt by alkali and then acid treatment. HCl/ HNO3 27 3. / Hydrometallurgy 133 (2013) 23–32 70% for Pt and Pd.99%) was produced by the calcination of the precipitate.25 Si) generated during nitric acid manufacturing by ammonia oxidation was studied. The spent cobalt-based catalyst of the Fischer–Tropsch (FT) process (wt.. which showed that particle sizes b100 μm and agitation speeds >700 rpm eliminated the internal and external mass-transfer resistances. widely used in the reforming process for the production of high-octane fuels containing 0. respectively.84 Re.K. Rh was recovered as potassium perrhenate with 94. High-purity Pt (99. revealing that the b 106 μm fraction is suitable for leaching Pt with aqua regia at a liquid/solid (L/S) ratio of 7.7–19. The sample was initially calcined at 800 °C to remove the wax. Jafarifar et al..5% was achieved by both routes. 8. Approximately 89% of the aluminum species present in the calcined spent catalyst was selectively dissolved in sodium hydroxide (6.3 for the hydrogen ion molarity in solution. The precipitate was decomposed by ignition to produce Pt powder with a purity of 97. Jha et al. (2009). The Re from the leach solution was then recovered by an anion exchange resin.%: 60–65 Al2O3. the sample was refluxed with aqua regia at a liquid/solid ratio of 5 for 2.3% using first and second method. (1985) employed hot sulfuric acid to dissolve Re and most of Al2O3 from the calcined Pt–Re–Al2O3 catalyst.15 Ca.5% and 98. 0. leaving other PGMs in the solution. such as sodium hydroxide. 1. The scrap produced in glass industries during sheets cutting contains Pt along with other elements (8636 mg/kg Ir. After leaching. as shown in Fig. Flow sheet for the recovery of platinum by hydrometallurgical process from platinum dust. 1. leaving Pt in the residue. The spent Ptaluminosilicate catalyst was treated in sulfuric acid to dissolve Al as aluminum sulfate. 18. 0. 16. The reaction order was 1.15 Cu. Commercial spent reforming catalysts were studied in aqua regia solution under atmospheric pressure at 100 °C for the dissolution of Pt by Baghalha et al.5 for Pt concentration in solid and 1. The leachate was an aqua regia-type solution in which part of the HCl content was replaced by aluminum chloride to lower the acid consumption.5 h. (2005) investigated two alternative methods for leaching the Pt/Rh bimetallic catalyst.5 h at 109 °C with 98% recovery (Barakat and Mahmoud.9% and 99. 1. Pt from the leach liquor was precipitated with ammonium chloride after dilution with water or HCl. 0. Leaching with aqua regia after acid/alkali treatment Different authors studied the dissolution of metals after treatment with acid to remove certain components of the spent material followed by aqua regia to dissolve Pt. 2. by direct precipitation as diammonium hexachloroplatinate and SX using trioctylamine in kerosene. as shown in Fig.9 Fe.2. resulting poor leaching efficiency. (1982) reported the recovery of Pt from the spent reforming and isomerization catalysts by selective dissolution of the base metals with 50% sulfuric acid followed by the leaching of Pt from the residue with aqua regia. the residue of the first-stage leaching was treated to recover Pt.43% Re and other impurities.9% for the direct and SX routes.%: 13. nitric acid/hydrochloric acid/sulfuric acid and aqua regia. Spent Pt gauze catalyst dust (wt. Pt and Co were leached from the residue obtained after the alkali pressure Platinum dust LEACHING FILTRATION Residue Alternative method Pt solution NH4Cl TOA SOLVENT EXTRACTION Pt PRECIPITATION NH4OH PRECIPITATION STRIPPING (NH4)2PtCl6 FILTRATION AND WASHING Filtrate for Rh recovery (NH4)2PtCl6 IGNITION IGNITION Pure Pt Pt powder Fig. respectively.9% recovery using the first and second methods.46 Ni. Pt was recovered as diammonium hexachloroplatinate after separating Rh. In the second case. 1985) was leached in a column using an aluminum chloride and hydrochloric acid solution with nitric acid as the oxidant at 90 °C. 2. The application of AlCl3 also reduces the required HCl content as a lixiviant without affecting the recovery.76% Pt. and the presence of aluminum ions will reduce the substrate dissolution rate. Leaching in the presence of hydrogen peroxide The leaching of Pt in aqua regia is not environmentally friendly method because of its toxic gas emissions according to the reactions (1)–(7) even in the absence of any dissolution process. minimizing the consumption of excess reagents. 1984). Their studies showed that up to 64% of the chloride ions from HCl can be substituted with AlCl3 without sacrificing the extraction of Pt and Pd. 1985. will be beneficial (Distin and Letowski.3. The solution could then be used to produce Pt sponge or Pt salt. which improves the PGM recovery. The effect of the aluminum chloride and nitric acid concentrations on the platinum dissolution yield was studied.2. / Hydrometallurgy 133 (2013) 23–32 leaching of Al by acid-aqua regia leaching or alkali pressure leachingaqua regia.1 M NaCl at 125 °C in 10 h. The spent automobile converter catalyst containing approximately 400 mg/t Pt and 150 mg/t Pd in alumina beads (Letowski and Distin.87% Rh. avoiding the significant loss of PGMs during grinding. These processes should be subjected to large-scale validation to assess their commercial viability.1 M NaCl at 125 °C. 1. may form NO depending on the solution condition. NO2. 0. Angelidis and Skouraki (1996) studied Pt recovery from spent Pt– NiO/Al2O3 industrial catalysts in the presence of aluminum chloride solutions. 1989). Leaching in the presence of chloride ions Many authors have investigated the leaching of Pt from spent catalysts in the presence of aluminum chloride to reduce the hydrochloric acid consumption and the generation of gases during dissolution with aqua regia (Letowski and Distin. 1987.28 M. such as non-volatile chloride salts. KCl. 2003). Nitrosyl chloride further decomposes into nitric oxide and chlorine.01% Ag and 0.14% Pd. The sample containing 16. the fumes over aqua regia contain Calcined spent catalyst NaOH BASIC LEACHING FLOCCULATION AND FILTRATION Leach liquor Sodium aluminate Sodium leached residue Nitric acid ACID LEACHING FLOCCULATION AND FILTRATION Leach liquor (Cobalt nitrate) Nitric acid leached residue CALCINATION Aqua-regia AQUA. The substitution of hydrochloric acid by aluminum chloride. During this dissolution. unlike other common chloride salts (NaCl. Therefore. Aluminum chloride is preferred because it provides three chloride ions per AlCl3 molecule. instead of aqua regia. does not affect the platinum dissolution yield while. . in addition to nitrosyl chloride and chlorine.K. toxic gases nitrosyl chloride (NOCl) and chlorine gas are formed. with low nitric acid concentration. with low concentrations of nitric acid as an oxidant. The spent catalysts (Pt–Rh or Pt–Pd–Rh alloys) from nitric acid manufacturing plants were processed to recover PGMs using a mixture of sulfuric acid and sodium chloride to replace aqua regia or autoclave leaching (Mahmoud. On mixing HCl and HNO3. CaCl2 or MgCl2). Almost all of the platinum species present in the nitric acid insoluble residue was dissolved in aqua regia at 80 °C and atmospheric pressure for 4 h to form a chloroplatinic acid solution. 0. A recovery of 99% Pt was obtained under optimum conditions of 60% H2SO4 and 0. 3. Angelidis (2001) reported the reduction leaching of automotive catalyst in the presence of hydrazine sulfate in sulfuric acid followed by oxidative leaching with HCl/AlCl3 to dissolve Pt and Rh. A flow-diagram for dissolving metal species from the calcined spent catalyst with basic and acidic lixiviants. During leaching with aqua regia above 70 °C. The reduction leaching destabilizes the refractory catalyst wash-coat. The replacement of a part of HCl with another complexing agent sources.REGIA LEACHING FLOCCULATION AND FILTRATION Leach liquor (Platinic acid) Aqua-regia residue Fig. another element of air pollution. 3.0012% Au and a large content of iron oxides and silica was ground and then leached with 60% sulfuric acid and 0. Jha et al. even from larger particles. high amounts of gaseous nitrogen oxides and HCl vapors are generated. NH4F Oxidizing agent: HNO3 Solid OXIDATION LEACHING FILTRATION Pt-Pd-Rh recovery ð11Þ Hydrogen pre-treatment Sample-B OXIDATION LEACHING FILTRATION HCl. 1977.. and over 99. NO gas generated in automobiles exhaust is also removed by using automobile catalyst.41 Sn. In the atmosphere. achieving a recovery of 95% Pt under the optimized lixiviant concentration with the oxidizing agent in a 10 HCl:1 H2O2 solution. hydrogen peroxide and nitric acid. / Hydrometallurgy 133 (2013) 23–32 nitric oxide. (2011) recently proposed a process flow sheet (Fig. 3. The reaction of Pt with sodium cyanide under pressure has been reported (Chen and Huang. A simplified flow diagram for recovery of Pt and other associated metals. Hancock et al. It is toxic and causes ozone layer depletion (Dessler. 1995a. Aberasturi et al.05 Fe. 0. The fluoride ion was also employed by adding NH4F. 2005. H2SO4. The process validated on a pilot scale (45 kg scale) (Kuczynski et al.37 Pt.37 Pt. The process is relatively environmentally friendly because Pt dissolution in this solution yields less hazardous gases. The study showed the possibility of replacing the HNO3 of aqua regia with hydrogen peroxide.30 Al) catalysts after oxidation in a furnace under air. The ground sample was thermally pretreated at 250 °C for 22 h before leaching in HCl and H2SO4 in the presence of oxidizing agents. Other associated metals.44 Li. 2006). The PGM from the leach solution was recovered by thermal hydrolysis of the cyanide complexes..%: 0. 1995b) obtained 95–97% Pt recovery from used pellet catalysts. The process could be easily adaptable for industrial application under the moderate experimental conditions.K.10 N NaOH and 1% NaCN leach solutions.005 Ni) with mixture of 10% HCl and 1% H2O2 at 70 °C for 2 h at 50 g/L pulp density after pretreatment at 800 °C. with 5% NaCN and 1% promoter at pH 11. The Pd and Rh recoveries were 94–95% and 64–81%. (1989) compared the dissolution of Pt from virgin and used monolith automotive catalysts using sodium cyanide solutions and reported recoveries of 75% and 95% of the PGM. 48. an important contributor of acid rains (Kennedy.8% PGM contained was removed. However.5 C. Recently. respectively. The presence of H2SO4 as a proton source also improves the leaching of Rh. 29 Sun and Lee (2011) also reported the leaching of the spent catalyst (wt. satisfying environmental regulations.77 V and has been employed to improve Pt leaching from spent catalysts and other materials. 1993) in two-stage autoclave leaching at 160 °C for 1 h with 0. from different types of car catalytic converter catalysts with honeycomb monolith supports with wash-coats onto which the PGMs are adsorbed. and the support material dissolved in 2–4 h at 60 °C.. 0. Leaching in cyanide solution Sodium cyanide has also been employed for the leaching of Pt and other associated metals of the spent materials because it forms stable complexes with PGMs (Atkinson et al. Jha et al. which decreased the solution–solid contact area. almost all of the PGM was leached in an autoclave above 250 °C in 1 h. H2SO4. However. 1992. 2Pt þ 8NaCN þ O2 þ 2H2 O ¼ 2Na2 ½PtðCNÞ4 þ 4NaOH: Atkinson et al. Therefore. 1992). The results were further validated on a 2 kg/day scale (Kuczynski et al. (2004) studied the recovery of Pt from Pt/Al2O3 (wt. 1995a. 1995b).. Pd and Rh are also leached in the presence of H2O2. The leaching of the calcined mass in the presence of HCl and fluoride ions was not effective. Under the optimum conditions of leaching with 5% NaCN at 160 °C in 1 h. A recovery of 95% was obtained by leaching at 90 °C for 6 h after thermal pre-treatment with both oxidizing agents. .. 10. 0. Chen and Huang. 0. respectively.4. The residue was also suitable for disposal. 3.15 Fe. (2009) studied the possibility of replacing aqua regia with HCl and H2O2 lixiviant for the dissolution of Pt from spent catalytic converters. the dissolution of Pt was effective in the presence of strong inorganic acids. it may further convert to nitric acid. The rapid decomposition of cyanide at elevated temperatures was found to be due to hydrolysis of cyanide to formate and ammonia.26 In. Further studies carried out in the presence of hydrogen peroxide improved the leaching kinetics to less than 1 h in the absence of strong mineral acid. 0. 3. which improved the dissolution efficiency by attacking the interface between the PGMs and the catalyst substrates. (2004) reported the leaching in cyanide solution and recovered 85% of Pt under the optimum conditions of a NaCN:catalyst Spent catalyst CRUSHING AND MILLING THERMAL PRE-TREATMENT Sample-A HCl. 0. 5. The dissolution chemistry and complex formation of PGMs in the solution were reported by Sibrell and Atkinson (1994).%: 0. including Pt. Kuczynski et al. Shams et al. recoveries of 97% and 85% of PGM were obtained from the virgin and used catalyst.28 Fe.M.. 0. A lower dissolution of 85–90% was found for the used monolith catalyst under the same experimental conditions in three leaching stages due to contamination with combustion byproducts and sintering of the used catalyst substrate.%: 0. 0.. Pt dissolution may be represented by the equation: þ − H2 O2 þ 2H þ 2e ↔2H2 O ð8Þ Pt þ 2H2 O2 þ 4HCl↔PtCl4 þ 4H2 O ð9Þ Pt þ 6HCl þ 2H2 O2 ↔½PtCl6 2− þ þ 2H þ 4H2 O: ð10Þ Kizilaslan et al.15Al.08 Pt. 3) for the dissolution of PGMs. NH4F Oxidizing agent: H2O2.60 Al) and Pt–Sn/Al2O3 (wt. A high recovery was obtained by leaching with NaCN at elevated temperatures in an autoclave (Desmond et al. 2000). 2006.85 Si.0 C. respectively. 50. The leach solution was used to separate the metals by solvent extraction and ion exchange. Chen et al. Hydrogen peroxide is a strong oxidizing agent with a standard electrode potential of 1. Solid Pt-Pd-Rh recovery Fig. 1992.8 and 80 °C in 1 h. 1991). Pinheiro et al. very little work has been reported so far on platinum/iodine leaching.I. • To replace the HNO3 oxidizing agent.R.J. T. The oxidation and reductions in this system are presented by the equations given below.. 0.40 V) is lower than that of other ionic species at 25 °C such as Pt4+ (1.657 V).R. 2011. The process is employed on the commercial scale to recover Pt. The pretreated material is then ground for subsequent leaching in cyanide solution. Barnard. hydrochloric acid in the presence of oxidizing agent. The “active” iodine species concentration decreased mostly due to conversion to “inactive” iodine–oxygen species and evaporation from the solution.D. The studies carried out under different conditions showed that the use of catalyst particles b106 μm and an impeller agitation speed above 700 rpm eliminated the mass-transfer effects during the leaching. PtCl62− (0. 4. but it requires high pressure to dissolve the metals. the following conclusions can be made. The aluminum of the catalyst support was also partially leached with the acid present in the lixiviant. Appl. Kuczynski. The cyanidation process has also been studied by Chen and Huang (2006) to recover PGMs from spent automotive catalysts containing 818. Leaching with iodide/iodine solution As the standard redox potentials of platinum in its iodide ion.28C. The leaching rate was also higher for higher HCl concentration and temperature. 505–513. Mahmoud (2007) used iodide solution for extracting precious metals under pressure in an autoclave. 2000). D.. The results show that the presence of coke does not have an adverse effect on platinum recovery in cyanide leaching. 0. Some of the spent materials may require thermal treatment before leaching under suitable conditions. HIO and IO− species then slowly disproportionate to IO3− and other highly oxidized iodine– oxygen species (Bard et al.98 LOI.A. other leaching agents. Larramendi. This process has potential use after validating the results for Pt dissolution on a larger scale. the dissolution of Pt using iodine/iodide solutions is more promising than the other halogen systems (Bard et al. In the cyanide dissolution of PGMs. which are ranked as Rh(CN)63− >Pd(CN)42− >Pt(CN)42−. Larramendi. As the leaching was slow at room temperature and pressure. The process consumes a large amount of acid to leach out the base metals and the alkali used to dissolve alumina and requires high temperature and pressure. Meng and Han (1996) reported the leaching behavior of Pt powder in iodide solutions with oxygen.N. 0. • The studies carried out in different lixiviants. Sodium cyanide has also been used for the leaching of Pt from spent catalyst. and minor constituents) using iodide solutions from 25 to 95 °C. in which. are also effective as leaching agents for the dissolution of Pt. E. the reaction rate has been proposed to be controlled by a surface chemical reaction. and in practice. 516.8 g/t Rh. (2006) reported the recovery of Pt along with Pd and Rh from spent automotive catalysts by pressure alkaline treatment followed by cyanide leaching. sodium cyanide and iodide solution. 2001. D. 1996. 1985). Similarly. Recovery of PGM from virgin automotive catalyst by cyanide leaching. 0. such as sodium cyanide and iodide solutions. sulfuric acid and salts of chloride ions such as AlCl3 or NaCl have been employed to form stable chloro-complex without affecting the efficiency of Pt leaching. Pd and Rh from different spent catalysts and electronic scrap.D. Development of a laboratory scale hydrometallurgical procedure for the recovery of Pt and Rh from spent automotive catalysts. Top. I3−.15 V). L. C. − 2− − PtðsÞ þ 6I ↔PtI6 þ 4e − − − I3 þ 2e ↔3I : ð12Þ ð13Þ Although the iodide system is promising. Skouraki. The environmental impact of these processes must be observed for the selection of a suitable process based on the presence of impurities and other associated constituents present in the spent materials and effluent generation. I3−).J... Recovery by hydrometallurgical extraction of the platinum-group metals from car catalytic convertors. Jha et al..3 g/t Pt. The recovered metallic powder is mainly platinum.N. The resin on which the platinum complex is adsorbed is dried and burned in an oxidizing atmosphere at 800–850 °C. Angelidis. R. there is no need for the decoking of spent catalysts in this method.B. I2.. PtI62−.. Walters.M. I.24 Re. The leaching of Pt was controlled by the surface reaction. TiO2. T. the economy of the process needs further improvement due to the dissolution of the alumina matrix and their separation. 1989. References Aberasturi. T. Desmond. 16 (17). G.. Miner. R. using acidic and alkaline solutions. Acknowledgments The paper is based on the Basic Research Project of the Korea Institute of Geoscience and Mineral Resources (KIGAM) funded by the Ministry of Science and Technology of Korea.5. • Aqua regia has been studied by several authors to leach Pt and other PGMs. The desired leaching of the PGMs requires high temperature and pressure. Catal. However. and IO− readily form. However. • To reduce the emission of HCl fumes during the leaching. 1–4. Catal.. the reaction occurs at higher temperatures than gold because the metallic bonding strength of PGMs is higher than that of gold and a surface oxide passivating layer is present. 24. • An alternative approach to dissolving the substrate using sulfuric acid or alkali has been proposed.19 SiO2. which could be subsequently leached in aqua regia to recover Pt.. the studies were carried out at elevated temperatures and pressures. Rojo. 3.744 V) and PtBr62− (0. similar to the gold cyanide reaction mechanism (Wadsworth et al. such as aqua regia. the process suffers from an environmental viewpoint as it generates NOx and chlorine and acid fumes during leaching due to the presence of HNO3 in the leaching agent. Although the Pt leaching rate is high in aqua regia.. 1985).7 g/t Pd and 213.30 S. 5. The leaching rate increases with increasing initial iodine–iodide concentration and liquid:solid ratio because they increase the concentration of the active iodine species (HIO. Conclusions Based on this review of the leaching of platinum from different waste materials. In: Austin.P.. HIO.30 M. These studies showed that the PGM metals are liberated from their carrier under high-temperature and pressure treatment with NaOH. • The above-mentioned processes must be evaluated on a large scale before commercial exploitation.%: 91. 140–180 °C in pH 8–9 in 1 h from the spent dehydrogenation catalyst. Angelidis. A.. Eng. particularly spent catalysts.. The consumption of cyanide is also high.. leaving Pt in the residue. 387–395. the aqueous ions I−. The dissolved Pt was recovered using an anion exchange resin.9 Al2O3. (0. Preliminary studies of platinum dissolution from a spent industrial catalyst. Pt extraction by cyanidation exhibits poor kinetics at room temperature and atmospheric pressure.K. the metal recoveries were 96% Pt. 98% Pd and 92% Rh. Atkinson. 142. H2O2 also has potential to be used for the leaching of Pt.D. . Zanjani and Baghalha (2009) reported the Pt recovery from the spent reforming catalysts (wt. Pinedo. The metallic platinum was finely dispersed on the walls of the nano pores of the gamma alumina support. I2(aq). J. 0. showing a cyanide leaching order of Pt>Pd>Rh due to the metal bonding strength of their complexes. A high concentration of HCl in the leaching solution also generates fumes and Cl2 gas.. Huang et al. as it is affected by the composition of catalyst substrate. showed the possibilities of leaching of Pt and other associated metals. A Gen. Under the optimized conditions. The leaching of the Pt is also effective in iodide solutions. The major platinum-iodide ion is PtI62− under acidic conditions.24 Pt. / Hydrometallurgy 133 (2013) 23–32 weight ratio of 2:1. This difference is due to the formation of stable Pt–iodide complexes more easily at lower potentials.. H. M. pp. S. Hydrometallurgy 95. J. J. Does interfacial charge transfer compete with charge carrier recombination? 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