Soil chemical and mineralogical principles in rehabilitation of infertile copper mine tailings for growing crops in China

In China approximately 20,000 hectares of land are degraded each year by mining and lost to agricultural production or other valuable uses. Two copper mines at Yuanqu, Shanxi Province, and Tong Ling, Anhui Province, were selected as pilot projects for an AusAID-funded mine waste rehabilitation project. The tailings of these mines made an inhospitable environment for plant growth, with sparse volunteer weeds of a few species colonizing the Yuanqu tailings, and no plants colonising the Tong Ling site. The main soil deficiencies were: (a) complete absence of available P and very little available N, (b) extremely small water holding capacity, (c) close to zero organic matter and zero cohesion, (d) extremely small cation exchange capacity, and (e) alkaline pH due to large amounts of calcite and dolomite. In addition, the tailings contained significant concentrations of copper and cobalt, which were potentially of concern if the crops to be grown were to accumulate these to dangerous concentrations. We mixed the tailings with local loess, containing 35% clay, adding fertilizer, and experimented with green manures (sudax-lupins, white clover-perennial rye grass, mung beans) to amend the tailings and make crops grow. We also used geochemical theory to assess solubility of the heavy metals and predict their availability to crops. Good results were obtained with a range of crops: peanuts, sorghum, and winter wheat. The sudax green manure had a beneficial effect lasting beyond the first crop.