College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QF, UK.
College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QF, UK.
Adv Colloid Interface Sci. 2019 Mar;265:14-28. doi: 10.1016/j.cis.2019.01.004. Epub 2019 Jan 24.
Apatite subspecies depend on their halogen and hydroxyl content; chlorapatite, hydroxylapatite and fluorapatite, with additional substitution of other elements within the lattice such as rare earth elements (REE), sodium, strontium and manganese also possible. Rare earth elements are vital to green and emerging technologies, with demand set to outstrip supply. Apatite provides a possible future source of REE. Processing rare earth deposits is often complex, with surface behaviour having a significant effect on the optimization of a process flow sheet. The effect of enrichment of natural apatite and the doping of synthetic apatite on surface behaviour can be determined by measuring the zeta potential and the isoelectric point of the mineral. In this paper, we review zeta potential studies of natural and synthetic apatite to determine the effect of elemental enrichment on surface behaviour. Fifty three studies of natural apatite and forty four studies of synthetic apatite were reviewed. The isoelectric point of apatite varied from pH 1 to pH 8.7, with studies of apatite specified to be >90% pure reducing the variation to pH 3 to pH 6.5. Of the four studies of rare earth enriched apatite found, three had IEP values between pH 3 and pH 4. A study of synthetic apatite showing enrichment of between 1 and 10% by the REE europium does not affect surface behaviour. However, no studies were found that investigated the effect of common REE processing reagents on REE enriched apatite zeta potentials. Therefore, in addition to comparing previous studies we also therefore present new zeta potential measurements of apatite from a REE enriched deposit under water and common flotation collector conditions. The IEP value of this apatite under water conditions was at pH 3.6, shifting to <3.5 under both hydroxamic acid and betacol conditions. When compared to previous studies, the behaviour of REE enriched apatite under collector conditions is similar to non-REE apatite. This result could be important for future processing of apatite enriched with REE, and therefore global apatite and rare earth supply.
磷灰石亚种取决于其卤素和羟基含量；氯磷灰石、羟磷灰石和氟磷灰石，晶格中还可能有其他元素的替代，如稀土元素（REE）、钠、锶和锰。稀土元素对绿色和新兴技术至关重要，需求有望超过供应。磷灰石可能是未来稀土元素的来源。稀土矿床的处理通常很复杂，表面行为对工艺流程的优化有重大影响。天然磷灰石的富集和合成磷灰石的掺杂对表面行为的影响可以通过测量矿物的动电电势和等电点来确定。在本文中，我们回顾了天然磷灰石和合成磷灰石的动电电势研究，以确定元素富集对表面行为的影响。综述了 53 项天然磷灰石和 44 项合成磷灰石的研究。磷灰石的等电点范围从 pH 1 到 pH 8.7，而指定为 >90%纯度的磷灰石研究将变化范围缩小到 pH 3 到 pH 6.5。在发现的 4 项稀土富集磷灰石研究中，有 3 项的等电点值在 pH 3 和 pH 4 之间。一项关于合成磷灰石的研究表明，在 REE 铕的富集程度在 1%到 10%之间不会影响表面行为。然而，没有研究发现调查常见的 REE 处理试剂对富含 REE 的磷灰石动电电势的影响。因此，除了比较以前的研究外，我们还根据水和常见浮选捕收剂条件下的 REE 富集矿床的新动电电势测量结果进行了介绍。这种磷灰石在水条件下的等电点值为 pH 3.6，在羟肟酸和 betacol 条件下降至 <3.5。与以前的研究相比，在捕收剂条件下富含 REE 的磷灰石的行为与非 REE 磷灰石相似。这一结果对于未来富含 REE 的磷灰石的加工以及全球磷灰石和稀土供应可能非常重要。
