High mercury leachate containing HgS22 − complex ion: Detoxifying solidification and high efficiency Hg extraction
Guanghua Lu , Changsheng Yue , Guibo Qiu , Min Guo , Fangqin Cheng , Mei Zhang
DOI:10.1016/j.jes.2018.01.026
Received October 20, 2017,Revised , Accepted January 26, 2018, Available online February 08, 2018
Volume 30,2018,Pages 177-184
Clean and efficient treatment of high-mercury leachate produced from remediation of mercury-polluted soil has become a huge challenge for environmental scientists. In this work, cement solidification was firstly adopted to treat the high-concentration mercury leachate, which had high alkalinity. Different mercury concentrations, namely 3.120 mg/L Hg mercury leachate and 9.243 mg/L Hg mercury concentrated leachate, were separately solidified by Portland cement. The results indicated that simply using the cement can properly solidify both the leachates to meet the waste landfill standard, with liquid (mL)/solid (g) ratio (L/S ratio) of 4:10–6:10. In order to make full use of mercury in the leachates, a Hg extraction method was subsequently carried out under different experimental parameters, such as temperature and pH value. It was shown that the Hg extraction ratio could reach as high as 99.84% and almost all the mercury in the leachate could be transformed to HgS precipitate; moreover, the Hg concentration in the treated leachate was reduced from 3.120 to 0.005 mg/L at pH 2.98 and 30°C, which was much less than the limit of the national standard, indicating that the leachate had been completely cleaned and could be discharged freely. Hence, simple cement solidification renders high-mercury leachate nontoxic, and the Hg extraction method can successfully recover the Hg and enable the residual leachate to be discharged safely.
