Acid Mine Drainage Treatment Using a Process Train with Laterite Mine Waste, Concrete Waste, and Limestone as Treatment Media

Abstract

Without treatment, the harmful effects of acid mine drainage (AMD) lead to the destruction of surrounding ecosystems, including serious health impacts to affected communities. Active methods, like chemical neutralization, are the most widely used approach to AMD management. However, these techniques require constant inputs of energy, chemicals, and manpower, which become unsustainable in the long-term. One promising and sustainable alternative for AMD management is to use passive treatment systems with locally available and waste-derived alkalinity-generating materials. In this study, the treatment of synthetic AMD with laterite mine waste (LMW), concrete waste, and limestone in a successive process train was elucidated, and the optimal process train configuration was determined. Six full factorial analyses were performed following a constant ratio of 0.75 mL AMD/g media with a 15-min retention time. The evolution of the pH, redox potential (Eh), total dissolved solids (TDS), heavy metals concentration, and sulfates concentrations were monitored as the basis for evaluating the treatment performance of each run. LMW had the highest metal and sulfates removal, while concrete waste caused the largest pH increase. A ranking system was utilized in which each parameter was normalized based on the Philippine effluent standards (DENR Administrative Order (DAO) 2016–08 and 2021–19). Run 4 (Limestone-LMW-Concrete waste) showed the best performance, that is, the pH increased from 1.35 to 8.08 and removed 39% Fe, 94% Ni, 72% Al, and 52% sulfate. With this, the process train is more effective to treat AMD, and the order of the media in treatment is significant.

Minimally Active Neutralization of Acid Mine Drainage through the Monte Carlo Method

“…In Ref. [10], used a tree-step process chain of laterite mine and concrete waste with CaO reagents, with four of their six samples achieving neutralization with pH vales of 7.01-8.08, while samples five and six overshot neutralization at 11.025 and 9.16, respectively [10].…”

“…As much previous work has shown that reductions in acidity, neutralization and moderate alkalinity help significantly in the decontamination of AMD through precipitation [16], it stands to reason that recent work might alter focus to finding different sustainable reagents that decontaminate AMD from heavy metals, even if they do not achieve neutralization or sulfur content reduction [9,10,15].…”

“…While these and other studies show that neutralizing agents are effective at reducing mineral contamination through precipitation [10,15], with [16], listing the corresponding pH levels for twelve contaminating metals, of which eleven are below pH 8.5 [16], previous work also shows that controlling neutralization is difficult. Some studies could not effectively neutralize the acidity with other agents [17], while many overshot neutralization [11,13,14,18,19].…”

“…CaO is a traditional, and quite effective, neutralizing agent [8], but recent studies have sought to find more sustainable substitutions that are also waste products, such as waste concrete or basic oven furnace slag [9,10]. Another industrial byproduct, fly ash (FA), generated from coal mines, has proven an effective substitute, with [11],finding that FA increased the pH and reduced the concentrations of Fe, Al, Mn, and sulphate significantly.…”

“…Some studies could not effectively neutralize the acidity with other agents [17], while many overshot neutralization [11,13,14,18,19]. Likewise, studies show that achieving a 6.5-8.0 pH range does not remove another major contaminant, sulfur, in its many forms [9,10]. Thus, additional active methods, such as using a jet loop reactor [19], in situ and ex situ carbonization bubbling [13], or reverse osmosis [9], were required to further remediate the AMD for pH and sulfur content and to bring the treated water into compliance with international water reuse standards.…”