Abstract
The removal of cadmium(ii) pollution in surface water by a polymer enhanced ultrafiltration (PEUF) process was investigated. Three water soluble polymers, chitosan (CTS), polyvinyl alcohol (PVA) and polyacrylate sodium (PAAS), were selected for this study. Of the three polymers, PAAS had strong interactions with Cd2+, and the PEUF achieved a high removal of Cd2+; therefore, PAAS was used as a complexing agent for the simulated cadmium pollution experiment. Experiments were performed as a function of the aqueous pH, polymer/Cd2+ ratio (P/M), ionic strength and humic acid. Under optimum experimental conditions, the Cd2+ removal rate reached 100%. pH was the main factor affecting removal of Cd2+, which decreased to 60% at a pH of 4. The Cd2+ removal was found to decrease as NaCl and HA were added. The analysis showed that the mechanism of NaCl could be a compressed electric double layer, while the mechanism of HA and H+ was competitive complexation. Finally, UF membrane fouling, the dissociation of PAAS–Cd and the regeneration of PAAS were investigated. The results showed that the higher P/M was, the lower the pH, the higher the HA concentration, and the more serious the UF membrane fouling were. The dissociation rate of PAAS–Cd reached 99.8% at a pH of 2.5. When the P/M was 5, the removal rate of Cd reached 99.6% with the addition of 20% new PAAS in the regenerate. This result showed that the PEUF process could be a promising method for removing Cd pollution in surface water.
Highlights
Cadmium (Cd) is a common heavy metal in polluted water that mainly comes from the illegal discharging of cadmium deposits, nonferrous metal metallurgy and the electroplating process.[1,2,3] Contamination accidents caused by Cd are the most severe and common pollution incident
It was found that an increase in the polymer/Cd2+ ratio (P/M) resulted in higher Cd2+ removal for all polymers
When the humic acid (HA) in the feed water was 2 mg LÀ1, the Cd removal rate was greater than 99%, and the Cd concentration was lower than 0.005 mg LÀ1 in the permeate with P/M values of 5, 10 and 30, which could meet the safe drinking water standard in China
Summary
Cadmium (Cd) is a common heavy metal in polluted water that mainly comes from the illegal discharging of cadmium deposits, nonferrous metal metallurgy and the electroplating process.[1,2,3] Contamination accidents caused by Cd are the most severe and common pollution incident. Cd is referred to as the most toxic element among all heavy metals. Cd is extremely noxious to human health.[4,5,6] The European Union, America and China all have strict standards for heavy metal in drinking water, among which the concentration of cadmium should be lower than 0.005 mg LÀ1 in China drinking water standard.[7] In general, the addition of alkali to polluted water is the dominant method to treat Cd pollution. It is urgent to explore an efficient Cd removal
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