Alkaline Injection of Concentrated Sodium Hydroxide Solution into an Acidic Surface Mine Spoil Aquifer

Abstract

A series of NaOH solution injection experiments were performed as trials for in situ remediation of an acid-producing surface-mine spoil. Both 20 and 50% (w/w) concentrated NaOH solutions were employed. While the spoil immediately down-gradient of the injection wells was neutralized, only about 23% of the introduced Na was recovered at the spring discharge in 3 years of post-injection monitoring. This rate of transport was far slower than the estimated advection rates in the aquifer, indicating that substantial retardation of both Na and the associated alkalinity occurred. This retardation is ascribed to: precipitation of alkaline-earth carbonate hydroxide minerals, as well as metal hydroxide precipitates, consuming injected alkalinity; and reduction of hydraulic conductivity in the peralkaline (pH [ 13) ''plume'' region due to plugging by reaction products. It is likely that Na and alkalinity will continue to leak from this plume region for many years, but at too slow a rate to neutralize AMD at current concentrations. Future injection efforts of this type may be feasible but should use lower concentrations and should be focused further down-gradient, in closer proximity to the springs, where ground water velocities are higher.

Mine Wastes

“…The acid ground water may migrate through a carbonate aquifer, and the natural neutralization reactions can lead to decreased contaminant loads. Injection of sodium hydroxide into acid ground water may also be a successful treatment technique (Werner et al 2008). In addition, passive chemical or biological treatment systems can be emplaced for the remediation of contaminated ground waters.…”

Hydrogeological feasibility of mine water deep geological storage in Baotashan coarse sandstone: A case study in Ordos Basin

“…Besides, the large‐scale water injection and continuous storage of saline mine water has not been sufficiently studied. The previous studies mainly focus on the remediation of alkaline NaOH solution injection into the spoil aquifer of an acid‐producing coal mine (Aljoe & Hawkins, 1993; Werner et al, 2008), situ mine water treatment (Jenk et al, 2014), mine water storage in underground artificial dams (Gupta et al, 1987), voids and goaf (P. Li et al, 2018; Sammarco, 1995; Song et al, 2020), receding the regional groundwater depression cone, land subsidence and water resource loss induced by coal mining activities. Comparatively speaking, mine water deep injection and storage by drill holes is much cheaper than the conventional active and passive methods.…”

Acid mine drainage treatment with dunite

“…These factors include: chemical characteristics of the AMD, the quantity to be treated, climate, terrain, sludge characteristics and projected life of the facility. The chemicals usually used for AMD treatment include limestone, hydrated lime, soda ash, caustic soda and ammonia [4,5]. Each chemical has *Corresponding author.…”