SYNERGISTIC EFFECTS OF CHELATING PRECIPITATION AND FLOCCULATION ON REMOVAL OF CADMIUM AMINO-COMPLEX FROM WASTEWATER

摘要

A method based on the synergistic effects of chelat-ing precipitation and flocculation was developed for removal of cadmium amino-complex from wastewater. In this paper, 2,4,6-trimercaptotriazine (TMT) was used as chelating ligand. The influence of reaction time, added quantity of TMT, pH value, and initial ammonia concentrations on removal of [Cd(NH_3)_4]~(2+) were investigated. The synergistic effects by TMT and different inorganic coagulants, including aluminum sulfate (Al_2(SO4)_3), aluminum chloride (AlCl_3), ferric chloride (FeCl_3), aluminum poly-chloride (PAC) and poly aluminum ferric chloride (PAFC), were compared for removal of [Cd(NH_3)_4]~(2+) from waste-water. As a result, synergistic effects on removal of [Cd(NH_3)_4]~(2+) were most obvious when PAC and PAFC were added. When the added amount of PAC reached 80 and 60 mg/L, the leaving concentrations of Cd(II) were 0.08 and 0.06 mg/L. These residuals of Cd(II) were lower than the concentration limit value of cadmium. The Cd-TMT precipitate would not produce secondary pollution. This low-cost method was efficient and applied in removing [Cd(NH_3)_4]~(2+) from practical wastewater in some Chinese factories.