K₂MgSi₃O₈ 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.