Dissolution of jarosite [KFe3(SO4)2(OH)6] at pH 2 and 8: Insights from batch experiments and computational modelling

Abstract

Jarosite [KFe 3 (SO 4 ) 2 (OH) 6 ] is a mineral that is common in acidic, sulphate-rich environments, such as acid sulphate soils derived from pyrite-bearing sediments, weathering zones of sulphide ore deposits and acid mine or acid rock drainage (ARD/AMD) sites. The structure of jarosite is based on linear tetrahedral-octahedral-tetrahedral (T-O-T) sheets, made up from slightly distorted FeO 6 octahedra and SO 4 tetrahedra. Batch dissolution experiments carried out on synthetic jarosite at pH 2, to mimic environments affected by ARD/AMD, and at pH 8, to simulate ARD/AMD environments recently remediated with slaked lime (Ca(OH) 2 ), suggest first order dissolution kinetics. Both dissolution reactions are incongruent as revealed by non-ideal dissolution of the parent solids and, in the case of the pH 8 dissolution, because of a secondary goethite precipitate on the surface of the dissolving jarosite grains. The pH 2 dissolution yields only aqueous K, Fe and SO 4 . Aqueous, residual solid and computational modelling of the jarosite structure and surfaces using the GULP and MARVIN codes, respectively, show for the first time that there is selective dissolution of the A-and T-sites, which contain K and SO 4 , respectively, relative to Fe, which is located deep within the T-O-T jarosite structure. These results have implications for the chemistry of ARD/AMD waters, and for understanding reaction pathways of ARD/AMD mineral dissolution.

Investigating the Effects of Se Solid Phase Substitution in Jarosite Minerals Influenced by Bacterial Reductive Dissolution

“…As jarosite-minerals are inherently unstable under circumneutral conditions, the significant change in Eh was indicative of a rapid mineral dissolution. The low Fe aq concentrations support prior investigations on jarosite dissolution as Fe(III) exhibits very low solubility at circumneutral pH [8,35,36]. The Ferrozine method showed that all Fe aq was in the form of Fe(II) [37,38].…”

Synthesis, characterization and thermochemistry of synthetic Pb–As, Pb–Cu and Pb–Zn jarosites

“…2a-c) with those previously reported confirm that the phases synthesised are jarosite analogues and that no other phases have been detected (Baron and Palmer, 1996;Drouet and Navrotsky, 2003;Powers et al, 1975;Serna et al, 1986). The O-H stretching (v OH ) band in the region 2900 to 3700 cm -1 shifts toward lower frequencies for the synthetic Pb-As (3343 cm -1 ), Pb-Cu (3362 cm -1 ) and Pb-Zn jarosites (3357 cm -1 ), compared with end-member synthetic K-jarosite (3385 cm -1 ) (Smith et al, 2006). The synthetic Pb-As jarosite has a relatively low v OH vibration frequency (i.e., 1634 cm -1 ) due to the partial substitution of arsenate for sulphate; arsenate is represented in the spectra as two peaks at 813 and 855 cm -1 (these correspond to the v 1 (AsO 4 3-) and v 3 (AsO 4 3-) modes, respectively, Fig.…”

Identification of materials related to acid mine drainage using multi-source spectra at S. Domingos Mine, southeast Portugal

“…Although copiapite and jarosite appear as the minerals with the lowest pH values in the sulphide oxidation pathway (Nordstrom and Alpers, 1999;Smith et al, 2006), this split appears to confirm a higher pH precipitation value for jarosite, suggesting a threshold of pH values detectable in the spectral data. The correlation values (Table II) are only above ≥0.90 for the endmembers for this specific copiapite-alunite assemblage, depicting a strong isolated relationship.…”

“…6 ] form at pH values <3, and precipitate near sources of acidity that are also sources of iron and trace elements (Nordstrom and Alpers, 1999;Smith et al, 2006). However, jarosite may also precipitate at higher pH values of waters, i.e.…”

“…In the pathway of the solution, it is then possible to identify mineralogical sequences, e.g. copiapite-jarosite-goethitehematite, with an increasing pH ranging from <3 to >6 or equivalent mineral`s pH indicators depending of the chemical composition of leacheates (Bigham et al, 1996;Nordstrom and Alpers, 1999;Swayze et al, 2000;Montero et al, 2005;Smith et al, 2006). Using IS principles it is possible to identify the unique spectral absorption characteristics of such secondary iron minerals (Clark, 1999).…”