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16Blast-furnace slag and metakaolin were geopolymerised, modified with barium or treated with a 17 combination of these methods in order to obtain an efficient SO 4 2-sorbent for mine water treatment. 18Of prepared materials, barium-modified blast-furnace slag geopolymer (Ba-BFS-GP) exhibited the 19 highest SO 4 2-maximum sorption capacity (up to 119 mg g -1 ) and it compared also favourably to 20 materials reported in the literature. Therefore, Ba-BFS-GP was selected for further studies and the 21 factors affecting to the sorption efficiency were assessed. Several isotherms were applied to describe

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Sulfate (SO) is a ubiquitous anion in natural waters. It is not considered toxic, but it may be detrimental to freshwater species at elevated concentrations. Mining activities are one significant source of anthropogenic sulfate into natural waters, mainly due to the exposure of sulfide mineral ores to weathering. There are several strategies for mitigating sulfate release, starting from preventing sulfate formation in the first place and ending at several end-of-pipe treatment options. Currently, the most widely used sulfate-removal process is precipitation as gypsum (CaSO·2HO). However, the lowest reachable concentration is theoretically 1500 mg L SO due to gypsum's solubility. At the same time, several mines worldwide have significantly more stringent sulfate discharge limits. The purpose of this review is to examine the process options to reach low sulfate levels (< 1500 mg L) in mine effluents. Examples of such processes include alternative chemical precipitation methods, membrane technology, biological treatment, ion exchange, and adsorption. In addition, aqueous chemistry and current effluent standards concerning sulfate together with concentrate treatment and sulfur recovery are discussed.

Analcime and commercial zeolite were employed as a precursor for preparing sorbent material for SO4 2removal over barium modification. Three sorbents were prepared: barium-modified analcime (ANA-Na-Ba), barium-modified acid-washed analcime (ANA-Ac-Na-Ba) and bariummodified zeolite (ZSM5-Na-Ba). Of the prepared materials, ANA-Ac-Na-Ba was the most efficient sorbent material for SO4 2removal, with a maximum sorption uptake of 13.7 mg g -1 at room temperature. Batch sorption experiments were performed to evaluate the effect of initial pH, initial SO4 2concentration, sorbent dosage, temperature and contact time of sorption.Several isotherms were applied to describe the experimental results and Bi-Langmuir was found to provide the best correlation for adsorption of SO4 2on ANA-Ac-Na-Ba. Kinetic studies were applied for the most effective sorbent material, ANA-Ac-Na-Ba, and the results showed that the sorption process follows pseudo-second-order kinetics.