K ₂ MgSi ₃ O ₈ in Slow-Release Mineral Fertilizer Prepared by Sintering of By-Product of Red Mud-Based Flocculant

Because of the large amounts of iron and aluminum in red mud, which is a by-product of the alumina industry, aluminum and iron can be extracted by HCl or H2SO4 to produce inorganic flocculants. However, residues produced by acid leaching pose environmental problems. In this study, a slow-release mineral fertilizer K2MgSi3O8 is prepared at 1,000°C for 2 h by sintering the flocculant by-product based on red mud. The main mineral in the fertilizer is K2MgSi3O8, with an irregular blocky morphology. In distilled water, 0.50 mol/L HCl, and 20 g/L citric acid, the dissolution rates of K2O are 13.13%, 96.36%, and 81.46% and those of MgO are 2.03%, 70.94%, and 66.03%, respectively. Cumulative release values of K2O and MgO are 6.98% and 0.01% on the first day and 56.12% and 1.70% after 28 days, and the slow-release rates satisfy the Chinese standard for slow-release fertilizers. Hence, the mineral fertilizer K2MgSi3O8 based on the by-product of red mud is a potential slow-release fertilizer.