Treatment and reuse of process water with high suspended solids in low-grade iron ore dressing

Abstract

Abstract Removal of highly dispersed suspended solids (SS) from process water is critical for the sustainable production of iron ore dressing. However, it is difficult to handle high SS content process water that has multiple silicate components in a strongly dispersed system efficiently, using conventional flocculants alone. In this work, we compared the sedimentation performance and underlying mechanisms applicable when dosing suspended silicate minerals with different polyacrylamides (PAMs), and assessed the feasibility of a robust method using anionic PAM and calcium ions to remove SS. Preliminary analysis indicated that the main constituents of the SS were ultrafine quartz and chlorite particles, which severely interfered with separation behavior. Different PAMs exhibited diverse flocculation effects on chlorite and quartz, whereas only the combination of anionic PAM and calcium ions flocculated them effectively and simultaneously. Results from zeta potential and Fourier-transform infrared spectroscopy (FTIR) measurements suggested that flocculation was mainly affected by the affinity between the charges on the mineral surface and flocculant functional groups. Calcium ions acted as an activator for the adsorption of anionic PAM onto the quartz surface, through a chemical bridging effect. Response surface methodology (RSM), incorporating Box–Behnken design, was performed to explore the effects of reagent dosage and SS content on separation indices. Field application of this model in Sijiaying Iron Ore Mine, China, allowed optimal conditions to be established, which were 2.86\xa0mg/L anionic PAM and 213\xa0mg/L CaCl2, at pH 11. After applying these modifications, the quality of the process water became acceptable for long-term reuse, and higher grade (65.10%) and recovery (68.50%) were achieved. The proposed flocculation method and the main conclusions from our work can provide information and advice for similar low-grade iron ore mines.