In light of the consequences of global warming and population growth, access to safe drinking water becomes an ever greater challenge, in particular in low to middle income countries in arid regions. Moreover, mining which may cause acid mine drainage and heavy metal contamination puts further pressure on management of limited water resources. Hence, the development of cost effective water treatment methods is critical. Here, using batch reactor experiments we investigate the kinetics and mechanisms behind divalent Mn and trivalent Cr removal from sulfate fluids using natural fluorapatite at 35 °C. The results show that the fluorapatite dissolution rate depends on fluid pH, and that dissolution is the dominant mechanism in fluids with pH below 4. Apatite can thus serve as remediation to neutralize acidic fluids. Fluid pH of 4-6 triggers a dissolution-precipitation mechanism, in some cases following upon a dissolution-only period, with the formation of a metal phosphate. In these experiments, Cr removal is two to ten times faster than Mn removal given similar solution pH. The results demonstrate that natural apatite represents a promising, cost effective material for use in passive remediation of mining-induced contamination of soils and groundwater in arid regions.

中文翻译：

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天然氟磷灰石的溶解动力学以及在35°C下从硫酸盐溶液中去除Mn2 +和Cr3 +金属的能力。

鉴于全球变暖和人口增长的后果，获取安全饮用水成为越来越大的挑战，特别是在干旱地区的中低收入国家。此外，可能导致酸性矿山排水和重金属污染的采矿给有限的水资源管理带来了进一步的压力。因此，开发具有成本效益的水处理方法至关重要。在这里，使用间歇反应器实验，我们研究了在35°C下使用天然氟磷灰石从硫酸盐流体中去除二价Mn和三价Cr的动力学和机理。结果表明，氟磷灰石的溶解速率取决于液体的pH值，并且溶解是pH低于4的液体的主要机理。因此，磷灰石可以起到中和酸性流体的作用。液体pH值为4-6会触发溶解沉淀机制，在某些情况下，仅在溶解阶段之后，就会形成金属磷酸盐。在这些实验中，在类似的溶液pH值下，Cr的去除速度比Mn的去除速度快2至10倍。结果表明，天然磷灰石代表了一种有前途的，具有成本效益的材料，可用于被动修复干旱地区采矿引起的土壤和地下水污染。