The Ultrafiltration Effect And Influence Mechanism Of Modified Attapulgite Complexing Heavy Metal

Heavy metal pollution in waters is one of the most serious pollution to human health and environment.With the development of ecological civilization,heavy metal effluents treatment has become a hot topic.The complexation-ultrafiltration technology is effective to treat heavy metal wastewater with low energy consumption,less secondary pollution and simple to operate.It has widely application prospects since it meets the increasingly strict requirements of environmental laws and regulations.This experiment uses the attapulgite from Tianshui of Gansu Province as raw material of complexing agent and modified with Cetrimonium Bromide to make attapulgite colloid.The complexation-ultrafiltration experiment of attapulgite colloid with artificial heavy metal wastewater is to study the removal effectiveness of heavy metal and ultrafiltration membrane pollution by different initial pH value,different amount of attapulgite agent and different heavy metal salts and ultrafiltration membrane pollution were investigated.In complexation-ultrafiltration experiment at different initial pH(pH=3?5?7?9?11),the retention rate of heavy metals increases significantly with the increase of pH.During the treatment of single heavy metal(Pb2+ or Zn2+),when pH is more than 9,the retention rate of Zn2+is more than 97%and that of Pb2+ is more than 98%,and both the residual concentrations of Zn2+and Pb2+ meet the relevant national standards.To dealing with the compound heavy metals(Pb2+ and Zn2+),the average retention rate of single heavy metal is higher than that of compound heavy metal when pH is 3 to 5;when pH is 7,single Pb2+ retention rate is less than compound Pb2+ average retention rate,but single Zn2+retention rate is more than compound Zn2+average retention rate;when pH is more than 9,the average retention rate of single heavy metal is less than that of compound heavy metal,and both the residual concentrations of Zn2+and Pb2+ meet the relevant national standards.In the process of compound heavy metals(Pb2+ and Zn2+)treatment,attapulgite has priority to complex with Pb2+,when the pH was 7,the selective separation coefficient get to the maximum value.In complexation-ultrafiltration experiment with different amount of complexing agent(1.0 g/L?3.0 g/L?5.0 g/L?7.0 g/L and 10.0 g/L),the retention rate of Pb2+ is always more than 91%and the retention rate of Zn2+is always more than 71%.In the treatment of single heavy metal(Pb2+or Zn2+),the retention rate of Pb2+ is always more than 97%and the residual concentrations of Pb2+ meets the relevant national standards once the added complexing agent is more than 5.0 g/L.The retention rate of Zn2+is always more than 93%and the residual concentrations of Zn2+meets the relevant national standards once the added complexing agent is more than 7.0 g/L.In the treatment of compound heave metals(Pb2+and Zn2+),the amount of attapulgite is added from 1.0 g/L to 10.0 g/L,the average retention rate of single heavy metal is less than that of the compound heavy metals.To treat the compound heavy metals(Pb2+ and Zn2+),attapulgite has priority to complex with Pb2+,when the added amount is more than 5.0 mg/L,the selective separation coefficient get to the maximum data.In complexation-ultrafiltration experiment,sulfate and brominated salt can inhibit the removal of heavy metals.Acetate and chloride decrease the removing efficiency of heavy metal and increase the removing efficiency of heavy metal at high pH.Nitrate almost has no effect on the removal of heavy metal.To treat compound heavy metals(Pb2+ and Zn2+),the efficiency of selective of heavy metal salt on heavy metal from high to low is acetate,sulfate,bromine,chloride,nitrate.The heavy metal wastewater is treated by modified attapulgite complexation-ultrafiltration for 120 min,the membrane flux is decreasing with time running.A membrane resistance pollution model is set up to analyze the changes of friction with the change of pH and attapulgite amount.With the increase of pH,the membrane inherent resistance Rm is basically unchanged,but the proportion of the inherent resistance Rm is continously decreasing.With the increase of pH,the resistance Rp,r ratio of reversible polarization layer increases slightly and the ratio of the resistance Rp,ir of the irreversible polarization layer and irreversible pollution resistance Rf keeps on increasing.The inherent resistance Rm,the ratio of the resistance Rp,ir of the irreversible polarization layer,the irreversible pollution resistance Rf,all of them are increasing with the increase of pH.The total membrane resistance increases with the increase of pH.With the increase of attapulgite amount,the membrane inherent resistance Rm is almost no change,but the proportion of the inherent resistance Rm is continously decreasing.With the increase of attapulgite amount,the resistance Rp,r ratio of reversible polarization layer first increases slightly and then decrease slightly,the ratio of the resistance Rp,ir of the irreversible polarization layer is continously decreasing,the proportion of irreversible pollution resistance Rf is continously increasing.Rm,Rp,ir and Rf are continously increasing with the increase of attapulgite amount.The total membrane resistance increases with the increase of pH and attapulgite amount,the total membrane resistance of compound heavy metals Zn and Pb is more than that of single heavy metal.