Passive remediation of acid mine drainage using cryptocrystalline magnesite: A batch experimental and geochemical modelling approach

Abstract

Acid mine drainage is generated when mining activities expose sulphidic rock to water and oxygen leading to generation of sulphuric acid effluents rich in Fe, Al, SO 4 and Mn with minor concentrations of Zn, Cu, Mg, Ca, Pb depending on the geology of the rock hosting the minerals. These effluents must be collected and treated before release into surface water bodies. Mining companies are in constant search for cheaper, effective and efficient mine water treatment technologies. This study assessed the potential of applying magnesite as an initial remediation step in an integrated acid mine drainage (AMD) management system. Neutralization and metal attenuation was evaluated using batch laboratory experiments and simulations using geochemical modelling. Contact of AMD with cryptocrystalline magnesite for 60 min at 1 g: 100 mℓ S/L ratio led to an increase in pH, and a significant increase in metals attenuation. Sulphate concentration was reduced to ≈1 910 mg/ℓ. PH redox equilibrium (in C language) (PHREEQC) geochemical modelling results showed that metals precipitated out of solution to form complex mineral phases of oxy-hydroxysulphates, hydroxides, gypsum and dolomite. The results of this study showed that magnesite has potential to neutralize AMD, leading to the reduction of sulphate and precipitation of metals.

Application of magnesite–bentonite clay composite as an alternative technology for removal of arsenic from industrial effluents

“…The morphology by SEM showed the presence of spherical structures. Masindi (2014) has reported that magnesite contains a fraction of crystalline phases and a portion of amorphous phase. The presence of Mg, C, O, Si, and Ca confirms that the material under study is magnesite.…”

“…The study conducted by Sparks (1997) pointed out that aluminum and iron oxides have high PZC values (usually at pH 8). The high PZC in bentonite clay is an attribute of the presence of aluminum and iron oxide or (Masindi 2014). The pH pzc value of a material is a reflection of the individual pH pzc values of the components present.…”

“…Combination of magnesite and bentonite clay (composite) will increase the concentration of base cations that are suitable for arsenic adsorption, especially at basic conditions (Alloways 1995;Langmuir 1997). Recent studies have reported that the Yellow Star Quarries in the Kroonstad district, Cape Town, Republic of South Africa (RSA), contains 750,000 m 3 deposit of bentonite that can be projected to 67 years if it is mined at a rate of 4000 m 3 / month (Masindi 2014;Gitari 2014). The magnesite mine in Folovhodwe, Limpopo province, RSA, showed that the magnesite deposit is close to 18 mega tons of cryptocrystalline magnesite which can be mined for the next 50 years (Agnello 2003).…”

Mine Drainage Generation and Control Options

“…The potential of applying magnesite as an initial remediation step in an integrated AMD management system was evaluated for neutralization and metal attenuation using batch laboratory experiments and geochemical modeling (Masindi et al, 2015). It was found that magnesite had the potential to neutralize AMD, reduce sulfate, and precipitate metals.…”

Introductory Chapter: Coal Fly Ash and Its Application for Remediation of Acid Mine Drainage

“…Traditionally, the remediation of AMD has been carried out through a range of active and passive technologies. Active treatment technologies involve the use of alkaline reagents such as limestone and lime [21,22], and magnesite [23]. Some of the limitations of limestone treatment processes include armoring of limestone particles by amorphous ferric hydroxide precipitates which reduces the eiciency of treatment process and atains a maximum pH of 7 which leaves species such as Mg in solution [24].…”