Influence of pH on Crystallization point of Liquid Aluminium Sulphate 8% w/w (as Al !"# Liquid Aluminium Sulphate, 8% w/w (as Al2O3) is an inorganic, acidic chemical !t is used primaril" as a coagulant #or the treatment o# water $he alumina content is directl" related to the a%ilit" o# the chemical to remo&e organics, colour and other contaminants #rom the raw water $he 'ualit" (ontrol methodolog" relating to this product is go&erned %" standard !S )* +3,2-+... $his standard descri%es how the Aluminium and Alumina content should %e anal"sed /hen anal"sing liquid aluminium sulphate the two most important parameters are actual Aluminium 0 Alumina content and actual Acidit" content Anal"sis o# %oth o# these parameters are co&ered in !S )* +3,2-+... 1oth methods are wet chemistr" %ased !n the case o# Aluminium anal"sis the method principle is that #ull aluminium comple2ation with an e2cess o# )3$A occurs and direct aluminium content is measured %" titration o# the e2cess )3$A with a standard solution o# 4inc $he main reason that !S )* +3,2-+... requires this method to %e used is that normal atomic a%sorption measurement o# % w/w aluminium content incurs too man" margins o# error $hese include errors due to the massi&e dilutions required and also possi%le inter#erences (hemi#loc scienti#ic sta## a#ter man" "ears o# anal"sis ha&e come to realise that this anal"sis cannot %e routinel" carried out where sta## ma" not ha&e the time nor in#rastructure readil" a&aila%le and instead leads to plants ha&ing to outsource anal"sis usuall" carried out %" inappropriate methodolog" as outlined a%o&e !n order to ma5e li#e easier and cost e##ecti&e (hemi#loc, through anal"sis, recognised the relationship %etween p6 and Acidit" content Also the relationship %etween Speci#ic 7ra&it" and Alumina content (as Al2O3) at 5nown Acidities Attached are a series o# (ali%ration (harts $hese (ali%ration (harts allow 8lant Sta## to quic5l" determine the Alumina content o# an" sample $ree Acidity $he degree o# Acidit" (Sulphuric Acid e2cess) has an impact on the p6 o# the product As the degree o# Acidit" increases the p6 decreases $he e##ect that Acidit" has on Liquid Aluminium Sulphate is demonstrated in the (ali%ration (harts attached =) :rom this chart "ou can see that this Liquid Aluminium Sulphate at a densit" o# + 32.o( has an Alumina content (Al2O3) o# 8% w/w (hart 2 is deri&ed using <+ . 2 to .% w/w :ree Acidit" Liquid Aluminium Sulphate (p6 . to ) . g/l .o( has an Alumina content (Al2O3) o# > =8% w/w as Al2O3 NOTE Just because your Liquid Aluminium Sulphate has an specific gravity of 1 !"# g$l % "#o& or higher' that doesn(t al)ays guarantee that its *+ )$) as Al"O!. o C . 2 and 3 illustrates the relationship %etween Speci#ic 7ra&it" and Alumina (ontent at di##erent le&els o# Acidit" (hart + is deri&ed using . = to + 9) :rom this chart "ou can see that this Liquid Aluminium Sulphate at a densit" o# + 32. > 8@ >8 > >@ >> + 3+2 % Alumina + 3+3 + 3+9 + 3+@ + 3+= + 3+> + 3+8 + 3+. ? 2 . 2.Cali%ration Charts (harts +. + 32 + 32+ + 322 + 323 + 329 + 32@ + 32= + 32> + 328 Specific -ra(ity * .% w/w Acidit" Liquid Aluminium Sulphate (p6 + 9 to 2 2) :rom this chart "ou can see that *eutral Acidit" Liquid Aluminium Sulphate at a densit" o# + 32. 2.% w/w :ree Acidit" Liquid Aluminium Sulphate (p6 .@ 8 > . Chart & Aluminium Sulphate (neutral acidity# 'ensity (s) %Al !" * pH of &)+. 2.o( has an Alumina content (Al2O3) o# > 88% w/w as Al2O3 (hart 3 is deri&ed using + . g/l . g/l . 8 2@ 82 8 +@ 8+ 8 .@ >. 8 +@ 8+ 8 . o C >8 > >@ >> > =@ >= > @@ >@ > 9@ >9 > 3@ + 3+2 + 3+3 + 3+9 + 3+@ + 3+= + 3+> + 3+8 + 3+.)/. > 8@ >8 > >@ >> > =@ >= + 3+2 + 3+3 + 3+9 + 3+@ + 3+= + 3+> + 3+8 + 3+. 1 ). > 8@ % Alumina % Alumina 8 > .) . + 32 + 32+ + 322 + 323 + 329 + 32@ + 32= + 32> + 328 Specific -ra(ity * .Chart Aluminium Sulphate (.)/.&). > .@ >. o C .% w/w Acidity# 'ensity (s) %Al !" * pH of . 0 . + 32 + 32+ + 322 + 323 + 329 + 32@ + 32= + 32> + 328 Specific -ra(ity * .% w/w Acidity 'ensity (s) %Al !" * pH of .@ >. 0 &)+.@ Chart " Aluminium Sulphate ( &). 315 1. 2.40 .6 7.5 7.20 Specific Gravity @ 20oC :ree Sulphuric acid e2cess in aluminium sulphate tends to change man" o# the chacteristics o# aluminium sulphate 1elow are the main characteristic changesA &# Alumina content As demonstrated in (hart +.324 1.318 1.o( would ha&e a concentration o# 8% w/w (as Al2O3) As the degree of acidity increases .75 7.328 pH 0.32 1.35 1.2 8.60 .317 1.85 7.decreases.45 7.(hart 9 is a re#erence chart suita%le as a wor5ing tool to allow determination o# Alumina content (Al2O3) #or an" Liquid Aluminium Sulphate sample at &ar"ing :ree Acidit" concentrations Chart + Aluminium Sulphate Density vs.319 1.7 7.20 to 0. the alumina concentration at any particular density )ould be lo)er than the alumina concentration at the same density of neutral acidic liquid alum) $his is largel" due to the #act that sulphuric acid itsel# has a densit" o# + 89 (ie + litre o# sulphuric acid B +.25 8.323 1.326 1.313 1.321 1.327 1.55 7. g/l .15 8. neutral acidic aluminium sulphate with a densit" o# + 32.316 1.314 1.312 1.95 7.89.322 1.1.9 7.1 8.2.40 ph 1.60 pH 0.05 % Alumina 8 7. %Al2O3 8.65 7. g) So an" increase in acidit" would increase the densit" while decreasing the concentration o# the Alumina $his is the main reason that when measuring Speci#ic 7ra&it" o# Liquid Alum it is essential to simultaneousl" measure the acidit" !# an acidit" measurement is una&aila%le then at a minimum a p6 should %e measured :rom %oth the densit" and the p6 a much more accurate Alumina measurement can %e o%tained as outlined a%o&e .3 8.325 1.the p.4 7.8 7. ..9 stipulates that Liquid Aluminium Sulphate should ha&e a cr"stalli4ation point o# not less C >o( $he lower the % w/w Acidt" o# the Liquid Alum the greater the protection against cr"stalli4ation /e must emphasi4e that this quic5 chec5 anal"tical method is not a replacement #or the wet chemistr" anal"sis outlined in !S )* +3..oC) $his matter is o# great rele&ance to water treatment plants in !reland especiall" as we ha&e %ecome accustomed to su%4ero winter temperatures o# the last #ew "ears !S )* 8>8-2.# Crystallization 2oint $here are man" #actors that contri%ute to gi&e Liquid Aluminium Sulphate its (r"stalli4ation 8oint $he two most important areA a) (oncentration o# Alumina %) (oncentration o# Acidit" A general rule o# thum% is that the higher the concentration o# either or %oth Alumina 0 Acidit" then the higher the cr"stalli4ation point in degrees celcius A solution o# 8% w/w (as Al2O3) Liquid Aluminium Sulphate with neutral acidit" has a cr"stalli4ation point o# < >o( 3he more acidic the solution the hi4her the crystallization point %ecomes ie5 %ecomes closer to . %ut the charts ha&e %een deri&ed #rom anal"sis carried out %" the methods outlined in the standard and there#ore gi&e an accurate appro2imation #or #ast.2-+. cost e##ecti&e and regular con#irmation o# product supplied .