Research On Advanced Treatment Of Heavy Metal Wastewater By Modified Bentonite Technology

Modified bentonite that be prepared will be applied to the waste watercontaining heavy metals.The effluent of heavy mental (lead and cadmium) meet therequirements of reuse water quality and GB3838-2002Surface water environmentquality standard class III. The experimental selects the best way for the advancedtreatment of wastewater containing lead and cadmium from MnCl2, polyacrylamide(PAM), sodium polyacrylate (PAASS) and PAM-EDTA modified bentonite. The bestchoice is manganese modified bentonite to treat wastewater.Under the different of pH, the removal of Pb2+increases with pH increasing. Withthe adsorption time becoming longer, the equilibrium concentration of Pb2+decreased,the removal rate increased gradually.Compared with the economic cost and emissionstandards, the best adsorption performance of manganese modified bentonite for leadwas achieved under the following conditions. The removing rate could reach up to95%when pH value is6, absorbent dose is20mg/L, adsorption time is40min and coagulantdose is60mg/L. The effluent of cadmium concentration is less than0.042mg/L, lessthan0.05mg/L, reaching the requirement of GB3838-2002Surface water environmentquality standard class III.pH is an important factor to adsorpt Cd2+with manganese modified bentonite.With the pH value increasing,the equilibrium concentration of Cd2+reduced. With theamount of adsorbent increasing, the equilibrium concentration of Cd2+decreased. Theremoving rate could reach up to96.7%when pH value is8, absorbent dose is20mg/L,adsorption time is40min and coagulant dose is60mg/L. The effluent of cadmiumconcentration is less than0.0033mg/L, reaching the requirement of GB3838-2002Surface water environment quality standard class III.When wastewater containing lead and cadmium was treated with manganesemodified bentonite, there is competition between lead and cadmium adsorption. Theabsorption of lead is better than cadmium with modified bentonite. The best adsorptionperformance of manganese modified bentonite was achieved under the followingconditions. When pH value is8, absorbent dose is20mg/L, adsorption time is60minand coagulant dose is60mg/L. The effluent of lead concentration is less than 0.048mg/L, less than0.05mg/L, reaching the requirement of GB3838-2002Surfacewater environment quality standard class III. The effluent of cadmium concentration isless than0.0046mg/L, less than0.005mg/L, reaching the requirement of GB3838-2002Surface water environment quality standard class III.By manganese modified bentonite non-ferrous mining water was treated.Thewastewater go through regulation pool, mechanical reaction tank, mechanical agitationclarifier and filter. Manganese modified bentonite was added before wastewater wentthough mechanical reaction tank, and PAC was added before wastewater went thoughmmechanical agitation clarifier. The sludge was sent to the tailings after be thickened,dehydrated. By manganese modified bentonite non-ferrous mining water wastreated.With a capacity of400m3/h in a nonferrous mining mine water project as anexample to carry on the investment estimation, the project total investment is10.494million yuan; operation cost is0.35yuan/m3; The recovery period of the projectinvestment cost is about2.5years, and it has high economic benefits, social benefits andenvironmental benefits.