Department of Mining and Materials Engineering, McGill University, 3610 University Street, Montreal, QC, H3A 0C5, Canada.
Department of Chemical Engineering, McGill University, 3610 University Street, Montreal, QC, H3A 0C5, Canada.
Chemosphere. 2016 May;151:318-23. doi: 10.1016/j.chemosphere.2016.02.087. Epub 2016 Mar 15.
Currently, the co-precipitation of arsenate with ferric iron at molar ratios Fe(III)/As(V) ≥ 3 by lime neutralization produces tailings solids that are stable under oxic conditions. However not much is known about the stability of these hazardous co-precipitates under anoxic conditions. These can develop in tailings storage sites by the action of co-discharged reactive sulfides, organic reagent residuals or bacterial activity. The ferric matrix can then undergo reductive dissolution reactions, which could release arsenic into the pore water. Co-ions like aluminum could provide a redox-immune sink to scavenge any mobilized arsenic as a result of reduction of ferric. As such, in this work Fe(III)/As(V) = 4 and aluminum substituted Fe(III)/Al(III)/As(V) = 2/2/1 co-precipitates were produced in a mini continuous co-precipitation process circuit and subjected to excess sulfide addition under inert gas to evaluate their stability. It was found that the ferric-arsenate co-precipitate could retain up to 99% (30 mg/L in solution) of its arsenic content despite the high pH (10.5) and extremely reducing (Eh < -200 mV) environment. There was no significant reduction of arsenate and only 45% of ferric iron was reduced. Partial aluminum substitution was found to cut the amount of mobilized arsenic by 50% (down to 15 mg/L) hence mixed Fe(III)/Al(III)-arsenate co-precipitates may offer better resistance to reductive destabilization over the long term than all iron co-precipitates.
目前，通过石灰中和使砷酸盐与三价铁以摩尔比 Fe(III)/As(V)≥3 共沉淀产生的尾矿固体在氧化条件下是稳定的。然而，对于这些在缺氧条件下的危险共沉淀物的稳定性，人们知之甚少。这些沉淀物可能会在尾矿储存场所中通过协同排放的反应性硫化物、有机试剂残留或细菌活动而形成。然后，铁基质可能会经历还原溶解反应，这可能会将砷释放到孔隙水中。像铝这样的共离子可以提供一个氧化还原免疫的汇，以捕获由于铁还原而被释放的任何砷。因此，在这项工作中，以 Fe(III)/As(V) = 4 和铝取代的 Fe(III)/Al(III)/As(V) = 2/2/1 的摩尔比在小型连续共沉淀过程回路中产生共沉淀，并在惰性气体下添加过量的硫化物，以评估其稳定性。结果发现，尽管 pH 值很高（10.5）且还原条件非常强（Eh < -200 mV），但铁-砷酸盐共沉淀物仍能保留高达 99%（溶液中 30 mg/L）的砷含量。砷酸盐没有明显减少，只有 45%的铁被还原。发现部分铝取代可将释放的砷量减少 50%（降至 15 mg/L），因此混合 Fe(III)/Al(III)-砷酸盐共沉淀物可能比所有铁共沉淀物具有更好的长期还原不稳定性抗性。
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