Abstract
Metal contamination in groundwater often occurs in various industrial processes. Studies have confirmed that polysulfide could reduce hexavalent chromium to trivalent chromium, achieving the effect of in situ stabilization. For other metal contamination in groundwater, whether polysulfide also had a stabilizing ability to achieve in situ remediation. This research focused on metals in addition to chromium that often contaminated groundwater, including lead, nickel, zinc, copper, and cadmium, to explore the feasibility of using calcium polysulfide (CaSx) as an in situ stabilization technology for these metals’ contamination of groundwater. Results showed that CaSx had a great removal efficiency for metals lead, nickel, zinc, copper, and cadmium. However, for nickel, zinc, copper, and cadmium, when CaSx was added excessively, complexes would be formed, causing the result of re-dissolution, in turn reducing the removal efficiency. As it is difficult to accurately control the dosage of agents for in situ groundwater remediation, the concentration of re-dissolved nickel, zinc, copper, and cadmium may not be able to meet the groundwater control standards. CaSx had high lead removal efficiency and for a concentration of 100 mg/L, the dose of calcium polysulfide was more than the amount of 1/1200 (volume ratio of CaSx to groundwater). In addition, the removal rate was almost 100% and it would not cause re-dissolution due to excessive CaSx dosing. CaSx can be used as an in situ stabilization technique for lead-contaminated groundwater.
Highlights
IntroductionDue to the operation of high-concentration metal solutions, many industrial processes such as metal surface treatment, battery manufacturing, recycling, dyes manufacturing and so on often cause groundwater and soil contamination by metals when tanks and pipelines were damaged
This study explored the feasibility of using calcium polysulfide to remediate groundwater contaminated by metals such as lead, nickel, zinc, copper, and cadmium, while it was compared with hexavalent chromium
As for lead, when the dose of calcium polysulfide was at the amount of 1/2000, the removal rate could reach 87.5%
Summary
Due to the operation of high-concentration metal solutions, many industrial processes such as metal surface treatment, battery manufacturing, recycling, dyes manufacturing and so on often cause groundwater and soil contamination by metals when tanks and pipelines were damaged. Zinc, chromium, and nickel groundwater contamination often occurs in metal electroplating and surface treatment processes; lead contamination occurs in battery manufacturing and recycling processes; and chromium and cadmium contamination occurs in dyeing and colorant production processes. For sites with a clear contamination scope and high contamination concentration, the pumping and treating method has the advantages of easy operation and speeding up the efficiency [1]. For sites with a wide range of groundwater contamination and low contamination concentration, it was relatively economical and efficient to use in in situ stabilization. Chemical precipitation was the most commonly-applied method for in situ stabilization [1]
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