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摘要
Selective removal of pollutants from soil leaching wastewater is the key step to recovery of eluent. Sodium sulfide (Na2S), potassium ethylxanthate (PEX), and sodium dimethyl dithiocarbamate (DTC) were used as heavy metal precipitants to treat simulated wastewater from leaching electronic-waste contaminated soil. Based on the screening experiments that identified Na2S as an ideal heavy metal precipitant, the effects of initial pH value, reaction temperature and precipitant concentration on the separation of complexed heavy metals in Na2S were investigated. The reaction mechanism was investigated by software prediction and product characterization. The results showed that the separation order of citric acid complexed heavy metals by Na2S was Cu, Pb and Cd, in line with the sulfide solubility. The reaction temperature and initial pH value had no significant effect on the complexed heavy metals treated by Na2S. The removal rate of heavy metals was above 90%, and the recovery of citric acid remained about 95%. The results of predition by Visual MINTEQ software show that before S2- addition metal cations were mainly associated with H2CA-,HCA2- and CA3-, while after S2- addition, metal cations have been bonded with HS- or S2-. The scanning electron microscopy and Energy dispersive spectrum (SEM-EDS) indicated that sulfide precipitation mainly existed in agglomerated, clustered and disc-shaped forms with a 1:1 molar ratio between S2- and other metal cations; The result of X-Ray diffraction (XRD) analysis revealed the main precipitated product was the mixtures of CuS, CdS, PbS and CuPbS2. These collective results provide a newly technical knowledge for the leachate recovery from the heavy-metal-leaching wastewater. ? 2020, Science Press. All right reserved.
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