Contamination by trace elements resulted from abandoned mines presented a serious environmental concern and posed a significant threat to the environment and human health. Consequently, there has been an increasing effort for developing cost-effective technologies for minimizing the mobility of trace metals and their bioavailability in contaminated mine-tailing soils. Although the mechanisms involved in immobilization of heavy metals using phosphorus amendments have been intensively investigated, the implementation of this technology in the field for remediation of soils and vegetables contaminated by lead and zinc mining tailings is limited.
In this study, a field demonstration of this control technology was conducted at lead and zinc mining tailings heavily contaminated by lead (Pb). The main objective of this field experiment was to evaluate the effects of three different kinds of phosphorus fertilizers on pH and in-situ heavy metal immobilization of the soil, including single superphosphate (SSP), phosphate rock (PR), and calcium-magnesium phosphate (CMP), observe the changes of water-soluble fractionation in the contaminated soil in relation with Pb accumulation by cabbage, and evaluate the feasibility using phosphorus fertilizers for in-situ immobilization of heavy metals in the contaminated soil.
The three phosphorus fertilizers were added to the soil at a phosphorus equivalent application rate of 50, 300 and 500 g/m², respectively. The correlation between soil pH and water-soluble heavy metals (Pb, Zn, Cu, and Cd), and the correlation between water-soluble heavy metals and heavy metals uptake in cabbage were elaborated in this study. The efficiency of the three different phosphorus fertilizers in decreasing the bioavailability of heavy metals in soil was also evaluated.
It was showed that the addition of different phosphorus fertilizers and (SSP, CMP and PR) could decrease the watersoluble heavy metals (Pb, Zn, Cu and Cd) and heavy metals uptake by cabbage, and also change the pH values of soil. A negative correlation was observed between the pH values in soil and water-soluble heavy metals (Pb, Zn, Cu and Cd). The addition of PR at a phosphorus equivalent application rate of 500 g/m² was the most effective in reducing the water-soluble Pb and Cd (both of the water-soluble Pb and Cd had 66.7% reduction), compared with the other treatments. The addition of CMP at a phosphorus equivalent application rate of 500 g/m² was the most effective in reducing the water-soluble Zn and Cu (the water-soluble Zn and Cu in soil had 97.1% and 88.9% reduction, respectively). The Pb in the cabbage was reduced most significantly with the addition of PR at a phosphorus equivalent application rate of 500 g/m², which had 62% reduction. The addition of CMP at a phosphorus equivalent application rate of 500 g/m² was the most effective in reducing the Zn, Cu and Cd in the cabbage (the Zn, Cu and Cd in the cabbage had 57.4%, 49.7% and 46% reduction, respectively).
In conclusion, it is effective and feasible to use phosphorus fertilizers for controlling accumulation of heavy metals in cabbages of contaminated mine-tailings, and CMP will be a more effective amendment.