Abstract X‐ray photoelectron spectroscopy (XPS) was evaluated as a technique to study anion adsorption on soil minerals; in this case, the well‐characterized systems of phosphate, sulfate, and selenite adsorption on goethite (α‐FeOOH). X‐ray photoelectron spectroscopy measured directly the surface coverage, the form of the adsorbed species and substrate, and the pH dependence of adsorption. The results confirm the previously reported adsorption mode in which two A‐type hydroxyls are replaced by coordination of two of the oxygen atoms of the anion.
Abstract Cation exchange capacity increased with both air drying (25°C) and oven drying (105°C). The initial value of exchange acidity at field moisture determines whether exchange acidity increases or decreases after drying. Exchangeable bases, particularly calcium, increase with oven drying.
Un bilan global entre acidite et basicite de roches exploitees dans les mines suite a leur oxydation par traitement au H 2 O 2 a ete etabli par calculs fondes sur la quantite molaire des cations neutralisateurs (Na, K, Mg, Ca) et de S apte a generer l'acidite en utilisant le test NAG (generation globale d'acidite). Ces cations neutralisateurs seraient derives a la fois de silicates et de carbonates; dans les echantillons a faible teneur en carbonate (ANC c a r b < 5 kg H 2 SO 4 /t), il est clair que la capacite des silicates a neutraliser l'acide pourrait etre plus importante que celle des carbonates. Un tel test n'est pas recommande pour les echantillons qui possedent une proportion importante de soufre non apte a former un acide, de cations non aptes a neutraliser, ou de mineraux sulfures non aptes a generer de l'acidite, par exemple la galene.
Abstract Most rock extraction sites, including mine sites and building construction sites, require a plan to assess, and mitigate if present, the risk of acid mine drainage (AMD). AMD is typically the major environmental concern where sulfide minerals are present in the excavated material and AMD prediction and remediation is based on internationally-accepted acid-base accounting (ABA) tests of representative field samples. This paper demonstrates that standardized ABA tests may not always be provide the correct AMD classification for commonly occurring waste rocks containing low-pyrite and -carbonate due to mineralogic assumptions inherent in their design. The application of these standard ABA tests at a copper mine site in South Australia resulted in the classification of a portion of its waste material as potentially acid forming in apparent contradiction to long term field measurements. Full definition of the sulfide and silicate minerals enabled re-evaluation of the weathering reactions occurring. The overall rate of neutralisation due to silicate dissolution was found to always exceed the rate of acid generation, in agreement with field observations. Consequently, the waste rock was redefined as non-acid forming. The methods developed represent a significant advance in AMD prediction and more strategic, cost-effective environmental planning, with potential for reclassification of wastes with similar characteristics.
This study developed an industry-applicable, thermal decomposition methodology for quantification of carbonate mineral acid neutralisation capacity (ANCtherm-carb) for waste rock, tailings, and other mined materials. Standard titration-based methods for ANC can be compromised due to contributions from silicate minerals, ion exchange, Fe-rich carbonates, and other transition metal carbonates. C emission (CO2 and CO) was measured using IR in a N2 atmosphere. Cneut (wt%) was calculated using the C emission at 800 or 1000 °C minus the C emission at 400, 450 or 500 °C and the weight of sample prior to decomposition (Equation (2) of this manuscript). This value was then input into Equation (3) of this manuscript to calculate ANCtherm-carb. Good correlation of ANCtherm-carb for single-mineral carbonates with ANCcalc, calculated from bulk assay concentrations for Mg, K, Na, Ca, and Mn, was achieved. Thereafter, 18 waste rock samples were examined, resulting in the correlation of ANCtherm-carb versus non-standard ANCtitrate-carb (titration methodology adapted to focus on carbonate neutralisation only) with R2 = 0.96. This correlation is valid for samples containing both non-neutralising carbonates (siderite) and sources of neutralisation arising from non-carbonates (Mg-clay) within this waste rock system. Typically, mining operations use total C measurements for assessment of carbonate neutralisation potential in the block and mining model. This method provides an effective means to cheaply analyse for carbonate neutralisation potential with assignment of potentially acid-forming and non-acid-forming blocks to waste rock cells, etc.
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