Process for recovery and value addition of silica mineral values of distinctly siliceous mining rejects

Abstract

The mining and metal industries generate a variety of solid wastes from mining activities to finished products. Mining rejects of non-ferrous industries such as bauxite, manganese, gold, zinc, lead and copper mines are underutilized and low in demand as potential raw materials for metallurgical use. Largely these materials are in bulk use for landfilling and building materials without recovering relevant mineral values. Major reject materials such as jarosite, kaolinite, khondalite, alumogoethite and saprolite are rich sources of alumina and silica-bearing mineral phases with varying compositions of iron oxide as major constituents. In the present study, the chemical and mineralogy of some of these materials were assessed. The technical scope for recovering one of the low-cost mineral phases in the rejects such as silica was ascertained for the potential value addition in view of the large scope of utilization in glass, glass products, molten sand, cement, fibreglass, ceramic enamel, sandblasting, refractory and light concrete.The recovered silica was used as a low-cost precursor for making value-added nano-silicate suitable for various industrial applications. The paper discussed the significance of the chemical composition and mineralogy of the raw materials. The process steps involved in the selective beneficiation of silicate mineral phases are used for the stepwise removal of iron oxide and alumina followed by the preparation of sodium silicate. Chemical precipitation and separation of nano-silica followed by characterization of silica nano-particles by scanning electron microscopy (SEM) and inductively coupled plasma (ICP)-MS analysis was also elaborated. These SEM studies inferred that the silica particles size ranges from nanometer to micrometre depending on various factors such as acid concentration, ageing time and the nature of the precursor used. ICP-MS analysis revealed the purity of nano-silicate prepared from the reject material. The leached solution consisting of aluminium has been utilized for making alpha alumina based on the IPR-protected in-house process route to follow the concept of producing zero waste.