Biochar enhances the growth and physiological characteristics of Medicago sativa, Amaranthus caudatus and Zea mays in saline soils

Purpose. This research aims to characterize the Langkat quartz mineral, especially its impurities, and to study the effectiveness of fungal-based leaching methods to purify the mineral in order to improve the quartz quality for high-tech industrial applications. Methods. Quartz was firstly analyzed to identify the mineral and chemical impurities. Quartz purification and beneficiation was performed by direct bioleaching using live indigenous Aspergillus niger, indirect bioleaching using metabolic lixiviant of the fungus, and chemical leaching using analytical grade oxalic acid. Findings. The mineral composition of the Langkat quartz deposit is dominated by quartz mineral (93%) with minor amounts of orthoclase feldspar (KAlSi3O8, 5%) and calcite (CaCO3, 2%). The chemical composition comprises 98.1% SiO2 with metal impurities of 0.8% Fe2O3, 0.29% Al2O3, 0.03% NiO, 0.028% Cr2O3 and 0.063% CuO, indicating that quartz is still not enough for advanced material production industry. The bioleaching process removes up to 98% of iron (Fe2O3) from the original quartz sample, and completely removes other metals within eight days of the process by direct bioleaching and eight hours by indirect bioleaching. The content of Fe2O3 and other metals in the treated quartz meets the specifications of high purity quartz (≤ 0.05%) for advanced material production industry. Meanwhile, chemical leaching using 0.2 M oxalic acid removes 96.9% of iron and 92.8% of aluminium. Originality. Comparison of the bioleaching potential of present indigenous Aspergillus niger with some of the previous studies shows that this strain has a higher ability to remove metal impurities from quartz in a much shorter processing time (8 hours instead of weeks or months) than most of the previously published microorganisms. Practical implications. The experimental result of this research provides significant potential for using a fungus-based purification approach to obtain high-purity quartz to be used in a high-value-added modern commercial product.