聚合物强化超滤技术分离Hg2+和Cd2+的研究

以聚丙烯酸钠为络合剂,研究Hg2+和Cd2+混合溶液的络合超滤分离行为.考察了pH值、负载比(LR)及外加盐浓度对混合体系分离的影响.结果表明,当pH值从5增大到7.5时,2种离子分离系数(S)逐渐下降,最适pH值为5;当LR从0.01增大到2时,S逐渐升高到最大值,此后迅速降低,LR=1.5时S达到最大值;Na2SO4的加入影响S值.控制混合溶液pH=5及LR=1.5,当体积浓缩因子为15时,截留液汞浓度(Cr, Hg)从30mg/L线性递增至444.9mg/L,截留液镉浓度(Cr, Cd)仅从30mg/L升高至35.4mg/L,S值约为227.浓缩液随着洗涤水体积增大,Cr, Hg基本不变,而Cr, Cd下降至5.24mg/L.收集各渗透液,调整至pH=6及LR=0.033予以浓缩,浓缩13倍时,Cr, Cd从27.37mg/L升高到354.7mg/L.

Separation of Hg2+ and Cd2+ by using polymer-enhanced ultrafiltration

Polymer-enhanced ultrafiltration was investigated to separate selectively Hg2+ and Cd2+ from aqueous solutions by using poly (acrylic acid) sodium salt as a complexing agent. Effects of pH, loading ratio (LR) and the added salt on separation coefficient (S) were investigated. When pH increased from 5 to 7.5, S decreased gradually. Controlling pH=5 was helpful to achieve the selective separation. At LR between 0.01 and 2, S increased with LR, reached a maximum value, and then decreased rapidly. It was preferable for the selective separation to control LR=1.5. S changed in the present of sodium sulfate. A concentration experiment was carried out at pH=5 and LR=1.5. When volume concentration factor (VCF) reached 15, mercury concentration in the retentate (Cr, Hg) increased linearly from 30 mg/L to 444.9 mg/L, whereas cadmium concentration in the retentate (Cr, Cd) changed only from 30 mg/L to 35.4 mg/L. S was about 227. Then, the final concentrated solution was used to study the process of washing. With increasing the washing water volume, Cr, Hg did not change, but Cr, Cd decreased rapidly to 5.24 mg/L. Further, another concentration experiment was performed at pH=6 and LR=0.033 by using all permeate solutions. At VCF=13, Cr, Cd increased from 27.37 mg/L to 354.7 mg/L.