Acid mine drainage (AMD) is a serious environmental problem caused by the weathering of sulfur-rich minerals found in mine sites, typically pyrite. Passive treatment methods have been extensively studied exploring various materials and treatment systems. Limestone is typically used as neutralizing media through open channels or anoxic limestone drains. However, the armouring that occurs when heavy metals precipitate on the surface restricts the lifespan of limestone treatment systems to 15-20 years. Goethite has been characterized to be a good adsorbent of heavy metals found in wastewater. It is abundant in a layer of nickel laterite deposit which are considered mine wastes due to the low amount of nickel present. This study investigates the performance of locally available nickel laterite ore rock, limestone, fly ash, and cement waste as media for AMD neutralization. The treatment efficiency are evaluated based on the physiochemical properties of the AMD, namely: pH, redox potential (ORP), conductivity, total dissolved solids (TDS), and dissolved oxygen (DO).

Acid mine drainage (AMD) generated from the mining industry elevates environmental concerns due to the pollution and contamination it causes to bodies of water. Over the years, passive treatment of AMD using alkalinity-generating materials have been widely studied with pH neutralization as its commonly observed mechanism. During the treatment process, heavy metal removal is also promoted by precipitation due to pH change or through adsorption facilitated by the mineral component of the materials. In this study, four materials were used and investigated: (1) a low grade ore (LGO) made up of goethite, calcium oxide, and manganese aluminum oxide (2–3) limestone and concrete aggregates (CA) composed of calcite, and (4) fly ash consisting of quartz, hematite, and magnetite. The performance of each alkalinity-generating agent at varying AMD/media ratios was based on the change in pH, total dissolved solids (TDS), oxidation reduction potential (EH); and heavy metals (Fe, Ni, and Al) removal and sulfate concentration reduction. Concrete aggregate displayed the most significant effect in treating AMD after raising the pH to 12.42 and removing 99% Fe, 99% Ni, 96% Al, and 57% sulfates. Afterwards, the efficiency of CA at various particle sizes were evaluated over 1 h. The smallest range at 2.00–3.35mm was observed to be most effective after 60 min, raising the pH to 6.78 and reducing 94% Fe, 78% Ni, and 92% Al, but only 28% sulfates. Larger particles of CA were able to remove higher amounts of sulfate up to 57%, similar to the jar test. Overall, CA is an effective treatment media for neutralization; however, its performance can be complemented by a second media for heavy metal and sulfate removal.

Goethite is a dominant component of nickel laterite ores, which is capable of adsorbing metal ions in water. The potential of the unused low-grade nickel ore (LGO) to treat synthetic acid mine drainage (AMD) was investigated.LGO characterization identified the presence of goethite (α-FeOOH), calcium oxide (CaO), and manganese aluminum oxide. The performance of LGO for AMD treatment was evaluated using jar test and compared with limestone. At 0.5 ml AMD/g media, LGO increased the pH of AMD to 5.36 while limestone completely neutralized it. LGO removed more than 99% of Al and Fe, 94% of Ni, and 93% of sulfates compared to a 70% sulfate removal using limestone. The lower sulfate removal may be due to the armouring of the limestone surface. Furthermore, a batch test was conducted using both LGO and limestone as layered treatment media in an oxic and anoxic setup. Effluent pH remained constant while conductivity and TDS stabilize at 2,000 μS/cm and 1,000 ppm, respectively. Both setups achieved 99% removal of Fe and Al,~90% Ni removal, and between 70% and 80% sulfate removal. These results indicate that LGO is a possible alternative material to be used for heavy metal adsorption for AMD treatment.

A post-treatment approach using common mushroom (Agaricus bisporus)derived chitosan was done to treat and purify a synthetic pretreated acid mine drainage (AMD) solution. Commercially available chitosan and laboratory-prepared chitosan were used as coagulants for post-treatment of AMD. Both chitosans were characterized by Fourier transform infrared (FTIR) and scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX). The treatment underwent a batch testing with parameters of mixing speed, mixing time, and chitosan loading. The removal of heavy metals focused on copper, iron, and nickel. The optimum parameters of the commercially available chitosan were then employed for the performance of the laboratory-prepared chitosan to evaluate its capability as a post-treatment agent for AMD.

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.