Settling of Iron and Aluminum Particles in Acid Solutions for Acid Drainage Remediation

Abstract

Mineral processing is intensive in water usage. Unfortunately, a large portion of this valuable asset is contaminated by toxic species that leach from tailings or mineral ore, leading to the formation of acid drainage. Water from acid drainages can still be recovered by passive environmentally friendly treatments. An underestimated passive treatment is the settling of harmful metals, such as iron and aluminum. In this sense, floc settling from acid drainage has not been well studied. The objective of this work is to research the phenomena governing iron and aluminum floc settling in acid drainage, particularly, the chemical conditions that promote settling. The settling velocity of iron and aluminum flocs was studied in a column at different pH and iron/aluminum concentrations. Stability was studied through zeta potential. According to the results, iron flocs settle faster than aluminum and aluminum+iron (mixed) flocs, and a lower pH promotes a higher settling velocity and greater floc stability, which a lower zeta potential (which favors aggregation) allows for. The results improve the understanding of the interactions between the chemical and physical processes involved in floc settling, which, in turn, can improve the optimization of water treatment design. Future experiments must include particle size distribution, floc porosity, and effective particle density of iron and/or aluminum particles in acid waters.