Reclamation of post-tin mining areas using forages: A strategy based on soil mineralogy, chemical properties and particle size of the refused materials

Abstract

The physical and chemical properties of refused materials in post-mining areas have received in-depth attention, while the mineralogy as a driver of the potential nutrient reserve has been ignored in reclamation practices. The objective of the study was to evaluate mineralogical, chemical, and physical properties and heavy metals of refused materials (spoil and tailings) as the basis for reclamation. Seven representative soil profiles were described and sampled to a depth of 130 cm for various soil analyses and to assess soil limiting factors for crop growth. Eleven forage species were tested in a field plot trial and their adaptability and biomass production against extreme limiting soil properties were evaluated for two consecutive growing seasons. Results showed that tin mining has drastically altered the soil texture from sandy clay loam under native conditions to loamy sand and sand under post-tin mining, resulting in serious unfavourable conditions for crop growth. Potential nutrient reserves have been depleted as revealed by the dominance of quartz minerals with small amounts of tourmaline, opaque minerals, zircon and garnet. Total elemental analysis using X-ray fluorescence (XRF) showed extreme high SiO2 content (92–96%) associated mainly with the dominance of quartz in the mineral constituents, and extremely low contents of Ca, Mg, P, K and S expressed as oxides (<0.2% altogether). This suggests that all nutrients are a severe constraint for crop growth. Among the analyzed total heavy metals, Cr2O3 contents were high (204–286 mg kg−1), while SnO contents were low (0–153 mg kg−1). However, the health risk is negligible because they were preserved in the structure of host minerals. Rehabilitation of post-tin mining was successfully performed using various forage types by implementing “a pot planting point system” accompanied by animal manure and complete fertilizer applications. Six out of the eleven forages tested, namely Cynodon dactylon, Pennisetum purpureum cv Mott, Brachiaria decumbens cv Humidicola, Pennisetum purpureum cv Taiwan, Brachiaria decumbens cv Mulato, and Paspalum atratum were recommended based on their high adaptability and significantly higher fresh biomass production (varying from 16.5 to 24.7 ton ha−1 season-1). Findings from this study provide alternatives for forage production systems to support livestock establishment. Soil mineralogy provides important information on nutrient reserves and should be considered part of an integral soil characterization including physical and chemical properties, and heavy metal contents of post-tin mining sites to ensure successful reclamation.