Immobilization of heavy metals in the saturated zone by sorption and in situ bioprecipitation processes

摘要

An ex-mining site located in Katowice, Poland, where silver, zinc and lead mining along with other activities took place for decades is now heavily contaminated with heavy metals. Especially the Quaternary and Triassic aquifers and surface water in the surrounding area are polluted. One serious risk is the threat of the contamination to drinking water, since the Triassic aquifer provides drinking water for more than 300 000 inhabitants. The main pollutants of concern are B, Ba, Zn, Cd, Cu, As and Sr. Remediation measures proposed for the Quaternary aquifer include a combination of natural attenuation, sorption barriers and in situ bioprecipitation. Dolomites, fly ash, and peat are considered as suitable adsorbent materials for removing barium and strontium from the contaminated groundwater. However, no adsorbent has been found to efficiently remove B. In situ bioprecipitation (ISBP), a process during which sulphate reducing bacteria are stimulated by the addition of various C-sources and sulphate is reduced to sulphides that concomitantly precipitate the heavy metals, has been tested on both clay and sand aquifer taken from the site. Zn and Cu, and sulphate were removed more quickly in the sandy aquifer material than in clay. In situ bioprecipitation combined with sorption was evaluated over a 150 days time period for the Triassic aquifer. Zeolites in combination with HRC or molasses gave the best results, removing 100 percent of Ba and Sr in less than 2 days and 35 percent of B after 150 days. However, no sulphate was removed under these conditions. In addition, when zeolite was combined with HRC, 100 percent Zn was removed in less than 2 days. Zn was also removed using MRC~R, lactate, and diatomic earth in combination with HRC~R or molasses. A combination of ISBP and sorption offers the potential to contain the metal contamination in this Triassic aquifer.