A multi-parameter titration method for the determination of formation pH for metal hydroxides

pH values of metal hydroxide formation were determined at 23 degreesC using a new multi-parameter scanning instrument employing simultaneous turbidity, conductivity and pH measuring capabilities. Results suggest that a combination of data from several simultaneously measured parameters provides a more reliable basis for the generation of quantitative data regarding formation pH and solubility, products of metal hydroxide precipitates than corresponding values obtained from single parameter measurements. The advantage rests in the possibility, to compare data from parallel sources as well as in the availability of characteristic information reflecting complementary aspects of the investigated systems. The present results obtained from alkaline titration of metal ion solutions coincide well with those found in literature, in particular when considering the great disparity among published values. Mean pK(sp)-values determined for 1, 5 and 10mM solutions of lead, cadmium, copper and zinc hydroxide are 18.7, 14.4, 19.7 and 16.0, respectively. The pH(IEP) values of metal hydroxide precipitates were determined from. stoichiometric solutions to be 11.1, 10.0, 8.8 and 10.3 for Pb(OH)(2)(s), Cd(OH)(2)(s), CU(OH)(2)(s) and Zn(OH)(2)(s), respectively, by zeta potential measurements. A dedicated instrument was used to measure the corresponding particle sizes, which corroborated with observations from the formation pH studies. (C) 2001 Elsevier Science Ltd. All rights reserved.