Immobilization of trace metals and arsenic by different soil additives: Evaluation by means of chemical extractions

Soils were amended with metal and arsenic (As) immobilizing soil additives [steel shots (SS 1% w/w), beringite (B 5% w/w), combination steel shots+beringite(SSB 1% SS + 5% B), hydroxyapatite (HA 0.5, 1, and 5% w/ w)]. The effectiveness of the additives in reducing metal and As mobility was assessed by means of chemical extractions with 1M calcium nitrate [Ca(NO3)(2)] in the case of metals and distilled water in the case of As. Among the additives tested, B, SSB, and 5% HA were most effective in reducing the mobility of cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn). Moreover, the effect of these additives was consistent in the different soils and their use might, therefore, be more or less universal. The lowest amount of As was extracted in soils amended with B, SS, and SSB. The effect of B was, however, soil dependent. The addition of HA led to higher As mobility due to the phosphate-arsenate competition for the sorption complex of the solid soil phase. Therefore, the use of I-IA at combined metal-as polluted sites has to be taken with care. Based on this study, it can be concluded that the addition of SSB seems the most promising treatment for the remediation of mixed metal-as polluted sites.