Response Surface Optimization And Model Establishment Of Copper Removal With Dithiocarboxylated Amine Methyl Polyacrylamide

Heavy metal pollution of water is one of the environmental problems that have been widely concerned in recent decades.The wastewater containing heavy metal must meet the relevant standards before it is discharged into water.Among all the heavy metal wastewater,the wastewater containing copper is the most common and the most abuntant wastewater.As a common method in chemical precipitation technology,chelating precipitation is widely concerned because of its simple operation and good flocculation effect.The flocc ulation effect mainly depends on the performance of chelating flocculant,so it is of great significance for the treatment of wastewater containing copper to develop an efficient and environmental friendly chelating flocculant.This paper is based on the previous research of the research group,polyacrylamide is employed as precursors,amidomethylated polyacrylamide（APAM）is synthesized by the aminomethylation of polyacrylamide（PAM）,and then the dithiocarboxyl groups（—CSS^-）are introduced into APAM to obtain the final product dithiocarboxylated amine methyl polyacrylamide（DTAPAM）.In this paper,the initial concentration of Cu²⁺,the ratio of Cu²⁺initial concentration to DTAPAM dosage,the initial pH value of water samples are taken as the influencing factors,and the Cu²⁺removal rate is taken as the response value,three response surface models are established under different Cu²⁺concentrations.The flocculation conditions of Cu²⁺removal by DTAPAM are optimized by response surface method.The effects of different influencing factors on Cu²⁺removal rate and the Cu²⁺removal model with DTAPAM are investigated.The fractal dimension of chelating flocs DTAPAM-Cu is also discussed.The main results are as follows:（1）The P values of DTAPAM removing Cu²⁺models under three Cu²⁺concentration ranges are all less than 0.05,and the models are significant.After response surface optimization,the optimal flocculation conditions of DTAPAM removing Cu²⁺model in low concentration section are as follows:the initial concentration of Cu²⁺is 15 mg/L,the ratio of Cu²⁺initial concentration to DTAPAM dosage is 1:6.7,and the initial pH value of water sample is 6.0;the optimal flocculation conditions of DTAPAM removing Cu²⁺model in middle concentration section are as follows:the initial concentration of Cu²⁺is 25 mg/L,the ratio of Cu²⁺initial concentration to DTAPAM dosage is 1:6.3,and the initial pH value of water sample is 6.0;the optimal flocculation conditions of DTAPAM removing Cu²⁺model in high concentration section are as follows:the initial concentration of Cu²⁺is 150 mg/L,the ratio of Cu²⁺initial concentration to DTAPAM dosage is 1:7.5,and the initial pH value of water sample is 4.0.（2）By comparing the Cu²⁺removal performance with DTAPAM under different concentration stages,it is found that DTAPAM has a better Cu²⁺removal effect in high concentration stage and worse Cu²⁺removal effect in low concentration stage.This indicates that DTAPAM is more suitable for the treatment of high concentration wastewater containing Cu²⁺.（3）The validation effect of DTAPAM removing Cu²⁺models is good under different concentration stages.When the initial concentration of Cu²⁺,the ratio of Cu²⁺initial concentration to DTAPAM dosage,and the pH value of the water sample changes respectively,the relative error between the measured Cu²⁺removal rate and the predicted value of the model is within±5%.（4）The coexisting inorganic cations(Na⁺,K⁺,Ca²⁺,and Mg²⁺)and inorganic anions(Cl^-,NO₃^-,and SO₄^2-)in the system have slight effect on the removal of Cu²⁺with DTAPAM.When the removal rate of Cu²⁺changes with the initial concentration of Cu²⁺or the ratio of the initial concentration of Cu²⁺to DTAPAM dosage,both inorganic cations and inorganic anions have little effect on the highest removal rate,but have greater effect on the low removal rate.（5）The coexisting sodium pyrophosphate,sodium citrate,EDTA and turbidity have certain effects on the removal of Cu²⁺with DTAPAM.When the initial concentration of Cu²⁺,the ratio of Cu²⁺initial concentration to the DTAPAM dosage,and the pH value of the water sample changes respectively,sodium pyrophosphate can promote the removal of Cu²⁺with DTAPAM.However,the sodium citrate,EDTA and turbidity can promote or inhibit the removal of Cu²⁺with DTAPAM,and the effects depend on the coexisting materials and their concentrations.（6）The effects of inorganic cations,inorganic anions,organic complexing agents and turbidity on the DTAPAM removing Cu²⁺models under different concentrations are different.The relative errors of the high-concentration range are basically distributed within±5%,the relative errors of the middle-concentration range are mostly distributed within±5%,and the relative errors of the low-concentration range are only partially distributed within±5%.Furthermore,the order is:low concentration range>medium concentration range>high concentration range.（7）When the initial concentration of Cu²⁺is 25 mg/L,the ratio of the initial concentration of Cu²⁺to the DTAPAM dosage is 1:6.3,and the pH value of the water sample is 2.0～6.0,the removal rate of Cu²⁺is 82.34%～99.12%,correspondingly,the fractal dimension of chelating floc DTAPAM-Cu is 1.4266～1.4575.This shows a good correlation,and there are similar rules under other influencing conditions,such as sodium pyrophosphate,sodium citrate,EDTA,and turbidity.