Effects of phosphate and citric acid on Pb adsorption by red soil colloids

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• 作者：Jichao Zuo ; Qingling Fu ; Xiaojuan Su ; Yonghong Liu ; Jun Zhu ; Hongqing Hu and Youjun Deng
• 刊名：Environmental Progress & Sustainable Energy
• 出版年：2016
• 出版时间：July 2016
• 年：2016
• 卷：35
• 期：4
• 页码：969-974
• 全文大小：237K
• ISSN：1944-7450

文摘

There are abundant organic acids in rhizospheric soil, which may interfere in the reaction between phosphate and heavy metals. Effects of phosphate on Pb²⁺ adsorption by red soil colloids(Ultisol) were studied in the presence of citric acid (Cit) through batch equilibrium experiments, Zeta potential and X-ray diffraction (XRD) analyses. Results showed that in the presence of different concentrations of phosphate (P), the peak-like curves of Pb²⁺ sorption was moved up even disappeared. When the Langmuir equation was used to model isothermal adsorption curve of Pb²⁺, the adsorption reaction constant (K), the maximum adsorption quantity (X_m) of several treatments were both in a decreasing order of 1.0 mmol/L P > 1.0 mmol/L P + 0.5 mmol/L Cit > 0.5 mmol/L Cit. Under the influence of citric acid, the Pb²⁺ adsorption amount increased at pH < 4.5, and then decreased gradually with pH increase. The order of Zeta potential reduction was: 1 mmol/L P + 0.5 mmol/L Cit > 0.5 mmol/L Cit > 1 mmol/L P, which were different from that of the Pb²⁺ adsorption amount, suggesting that the adsorption of Pb²⁺ was not only an electrical adsorption in the presence of P. XRD patterns proved that occurrence of pyromorphite for the treatment with 1.0 mmol/L P addition, whereas no lead phosphate peak was detected in other treatments. The mechanism of Pb²⁺ adsorbed in red soil colloids with addition of phosphate was primary formation of pyromorphite-like compounds. However, 0.5 mmol/L Cit inhibited the formation of pyromorphite.