TREATMENT OF FLY ASH/APC RESIDUES INCLUDING LEAD SALT RECOVERY

摘要

The present invention relates to a process for treating fly ash/APC residueschlorides, sulphates, earth alkali metals selected from the group consistingof calcium, potassium, and sodium, and heavy metals selected from the groupconsisting of lead, which residues are obtained from air pollution controlprocesses that utilize dry/semi-dry lime injection, such that said residuesmay be disposed of as non-hazardous materials. The process comprises thesequential steps of: (a) washing and agitating the fly ash/APC residue (20)with water (50) to form a residue slurry containing solubilized lead salts andcalcium chloride; (b) filtering (42) the residue slurry to remove a filtrate(46) having a pH of higher than about 11.8 and containing the solubilized leadsalts and calcium chloride; and (c) recovering a first calcium enriched filtercake (44). The solubilized lead salts are then removed from the filtrate bythe sub-steps of: (i) adding sufficient hydrochloric acid (58) to the filtrateto lower the pH thereof to between about 10 and 11; (ii) agitating thefiltrate until a colour change from white to yellow occurs; (iii) addingadditional sufficient hydrochloric acid to the filtrate so agitated to lowerthe pH to between about 7 and 8; (iv) filtering (82) the filtrate to remove abrine (86) containing calcium chloride; and (v) recovering a second yellowcoloured, lead enriched filter cake (84).