Influences of sulfate and/or silicate present in partially prehydrolyzed Al(III) flocculants on Al(III) speciation in diluted solutions

Influences of prehydrolysis in partially neutralized Al(III) flocculants containing of sulfate and/or silicate on Al(III) speciation are investigated. To this end, many flocculants were synthesized. They were prehydrolyzed with sodium aluminate in the presence of silicate and/or sulfate with increasing Si/Al and/or SO4/Al molar ratio and diluted to 0.1-0.01 M Al. Alkalimetric titration and Al-27 NMR spectroscopy were used to monitor the Al speciation. The results suggest that prehydrolysis with sodium aluminate reduces Al-13 concentration in comparison with the standard hydrolysis method. The silicate specifically inhibits Al-13 formation and promotes formation of unidentified soluble species. The sulfate indirectly inhibits Al-13 by promoting the formation of solid Al (oxi)hydroxide. In regard to the results presented here, it appears that Al-13 formation is unlikely for conditions of use of standard flocculants. (C) 1999 Elsevier Science B.V. All rights reserved.