Determining the optimal conditions for precipitation of hydroxides of impurity metals in purification of waste water

摘要

The hydrolysis constants (log kappa) and degrees of hydrolysis (log alpha') of different metals are calculated on the basis of the values of the stability constants of hydroxocomplexes of basic impurity metals (Cu, Zn, Fe). It is shown that for practically all stages of hydrolysis the Fe~(2+) ions possess least values of log k, followed (in increasing order) by Cu~(2+), Zn~(2+), and Fe~(3+). Similarly, the highest values of log alpha' are inherent to Fe~(3+), and the least, to Fe~(2+). Recharging of positively charged (zeta =7-11 mV) particles of hydroxides of Cu, Zn, and Fe(II) occurs in the interval of pH values 8.5-9.2, while for hydroxides of Fe(III) and Al, at pH approx = 7.5. The use of the coagulating agents and anion flocculants under study in the interval of pH values 8.5-9.0 significantly intensifies the process of precipitation of dispersed particles of hydroxides of impurity metals out of diluted pulps.