Immobilization of Pb, Cd, Cu and Zn in a Multi-Metal Contaminated Acidic Soil using Inorganic Amendment Mixtures

The objective of this study was to evaluate the effectiveness of inorganic amendment mixtures including zeolite, limestone and phosphate rock for the remediation of a multi-metal contaminated acidic soil. Firstly, a 40-day batch experiment using orthogonal design was conducted to select the best inorganic amendment mixtures for increasing soil pH and decreasing the mobility of Cd, Pb, Cu and Zn in soil. The application of mixture amendments all significantly increased soil pH and decreased the CaCl2-extractable Cd, NH4NO3-extractable Pb, Cu and Zn concentration. Among them, four kinds of inorganic amendment mixtures were selected for pot experiment with water spinach (Ipomoea aquatica F.), lettuce (Lactuca sativa L.) and Chinese flowering cabbage (Brassica campestris L.) which increased soil pH by 2.24-2.90 units and decreased the CaCl2-extractable Cd, NH4NO3-extractable Pb, Cu and Zn concentration by 96.77-100%, 98.64-99.83, 95.69-97.09 and 96.26-99.56%, respectively, and they all greatly improved plant growth and significantly reduced Cd, Pb, Cu and Zn concentration in the shoot of plants compared with the un-amended control. Furthermore, there was a significant positive correlation between the CaCl2-extractable Cd, NH4NO3-extractable Pb, Cu and Zn concentration in soil and their concentration in the shoot of plant (P < 0.05). Metal sequential fractionation data indicated that inorganic amendment mixtures substantially modified the partitioning of soil Cd, Pb, Cu and Zn from the easily exchangeable phase to less bioavailable Fe-Mn oxides bound and carbonate bound fractions. The result demonstrated that the application of inorganic amendment mixtures could offer an efficient way to immobilize heavy metals and improve plant growth in acidic multi-metal contaminated soils.