Competitive immobilization of Pb in an aqueous ternary-metals system by soluble phosphates with varying pH.
Chemical immobilization by phosphates has been widely and successfully applied to treat Pb in wastewater and contaminated soils. Pb in wastewaters and soils, however, always coexists with other heavy metals and their competitive reactions with phosphates have not been quantitatively and systematically studied. In this approach, immobilization of Pb, Zn, and Cd by mono-, di-, and tripotassium phosphate (KH2PO4, K2HPO4, and K3PO4) was observed in the single- and ternary-metals solutions. The immobilization rates of the three metals were determined by the residual concentration. The mineral composition and structure of the precipitates were characterized by powder X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The results indicated that competitive reaction occurred in Pb-Zn-Cd ternary system, with immobilization rates decrease of <3.6%, <78%, and <89% for Pb, Zn and Cd (molar ratios of P: metal <1), respectively, compared to single metal system. The reaction of Pb with three phosphates exhibited intense competitiveness and the phosphates had a stronger affinity for Pb when Cl(-) was added. Pb-phosphate minerals formed by KH2PO4 with the better crystalline characteristics and largest size were very stable with a low dissolution rate (<0.02%) in the solution of pH 2.88, compared to K2HPO4 and K3PO4. This study demonstrated that Pb could be firstly and effectively immobilized by phosphates in multi-metal solutions containing Pb, Zn and Cd. Moreover, the research provided the insight of the importance of phosphate with low pH (e.g. KH2PO4) and the presence of Cl(-) for more efficient immobilization of Pb in the multi-metals pollution system.
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; Engineering Research Center of Groundwater Pollution Control and Remediation, Ministry of Education, Beijing Normal University, Beijing 100875, China.
Zhuo
Z
Zhang
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; Engineering Research Center of Groundwater Pollution Control and Remediation, Ministry of Education, Beijing Normal University, Beijing 100875, China.
Jie
J
Ren
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; Engineering Research Center of Groundwater Pollution Control and Remediation, Ministry of Education, Beijing Normal University, Beijing 100875, China.
Mei
M
Wang
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
Xinlai
X
Song
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
Chao
C
Zhang
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
Jiayu
J
Chen
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
Fasheng
F
Li
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China. Electronic address: guogl@craes.org.cn.
Guanlin
G
Guo
D002104:Cadmium / Q000737:chemistry*; D052918:Environmental Restoration and Remediation; D006863:Hydrogen-Ion Concentration; D007854:Lead / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry*; D017680:Potassium Compounds / Q000737:chemistry*; D012995:Solubility; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D014961:X-Ray Diffraction; D015032:Zinc / Q000737:chemistry*
D008903:Minerals; D010710:Phosphates; D017680:Potassium Compounds; D014874:Water Pollutants, Chemical; D002104:Cadmium; D007854:Lead; C013216:potassium phosphate; D015032:Zinc
Competitive immobilization; Pb; Soluble phosphates; Ternary-metals solution; pH