Heavy metals in mine soils amended with sewage sludge

In order to reclaim a clay quarry, a topsoil material was mixed with gravel ly spoil at different ratios and with various rates of sewage sludge. The i nfluence of three spoil/topsoil ratios (1:1, 2:1 and 3:1) and three sludge rates (40, 80 and 120 t ha(-1)) on chemical properties of the resulting mat erial was investigated, with emphasis on heavy metal (Fe, Cu, Mn, Ni and Zn ) contents. The mixtures topsoil/spoil/sludge were water saturated and incu bated for 15 or 30 days in a chamber under controlled conditions. The incub ated samples were analysed for pH, total carbon and nitrogen, and total, av ailable, exchangeable and soluble heavy metals. The addition of spoil to th e topsoil increased the volume of material available, by utilizing an inert material unsuitable by itself to grow plants. The addition of sewage sludg e repaired the disadvantages of the spoil, increasing the pH and the organi c matter contents. The total heavy metal contents in the mixtures followed the sequence Fe much greater than Mn much greater than Zn, Cu > Ni. All exc ept Cu were within the ranges allowed for agricultural lands. The available heavy metals constituted a small fraction of total contents and decrease w ith time due to complexation and immobilization processes. The exchangeable and soluble fractions were almost negligible; only small amounts of Mn, Zn and Cu were detected. Therefore, the risk of contamination by heavy metals is insignificant in the conditions investigated. Copyright (C) 1999 John W iley & Sons, Ltd.