Hydrothermal precipitation from aqueous solutions containing iron(III), arsenate and sulphate
Hydrothermal precipitation from aqueous solutions containing iron(III), arsenate and sulphate
复制标题
DOI：
10.1007/978-94-011-1214-7_10
复制
发表时间：
1994
期刊：
影响因子：
--
通讯作者：
Pm Swash-;A. Monhemius
中科院分区：
文献类型：
--
作者：
Pm Swash-;A. Monhemius
从含不同比例Fe ~（3+）、SO_（43-）和SO_（42-）的溶液中沉淀出的固体的合成、表征和溶解度测试的系统程序，使各种砷相的相对稳定性得以经验地评估。90%以上的砷可从pH<1，Fe：As ≥1的溶液中在150 ℃以上沉淀;形成的固体是结晶的，通常由明确定义的化合物或化合物的混合物组成。虽然沉淀物的堆积度随着合成温度的增加而增加，但是由于形成了不同的化合物组，它们的稳定性并不总是相应地增加。形成的砷化合物包括臭葱石和两种未知的化合物，它们被命名为1型（Fe 2（HAsO 4）3-zH 2 O）和2型（Fe 4（AsO 4）3（OH）x（SO 4）y）。在高温下合成的化合物的稳定性（基于砷溶解度）的相对顺序为：2型003 D;臭葱石>砷铁水铁矿> 1型。当将这些高温结晶固体的稳定性与在环境温度和pH 5下沉淀的无定形砷酸铁（Fe：As >3：1）进行比较时，结晶固体稍微不太稳定。然而，结晶化合物中的砷含量（Fe：As = 1：1）比非晶沉淀物（Fe：As >3：1）高得多。后者的化合物主要由无定形的水铁矿组成，其在老化时可以结晶和重结晶，并且由于表面积和活性位点的减少而可能释放吸附的砷。因此，形成稳定的结晶化合物可能是一个更有吸引力的处置选择砷。
A systematic programme of synthesis, characterisation and solubility testing of solids precipitated from solutions containing various ratios of Fe3+, ASO43- and SO42- has enabled the relative stabilities of the various arsenical phases to be assessed empirically.Over 90% of the arsenic can be precipitated from solutions of pH<l, Fe:As ≥1, at temperatures above 150°C; the solids formed are crystalline and usually consist of well-defined compounds or mixtures of compounds. While the crystallinities of the precipitates increase with temperature of synthesis, their stabilities do not always increase correspondingly due to the formation of different suites of compounds. The arsenical compounds formed include scorodite and two unknown compounds that have been designated Type-1 (Fe2(HAsO4)3-zH2O) and Type-2 (Fe4(As04)3(OH)x(SO4)y). Crystalline ferrihydrite can also be formed from solutions containing high concentrations of iron and this can readily incorporate substantial amounts of arsenic.The relative order of stability (based on arsenic solubility) of the compounds synthesised at elevated temperatures is: Type-2 003D; Scorodite > Arsenical Ferrihydrite > Type-1. When a comparison is made of the stability of these high temperature crystalline solids with amorphous iron arsenates (Fe:As >3: 1) precipitated at ambient temperature and at pH 5, the crystalline solids are marginally less stable. However, the crystalline compounds contain considerably more arsenic (∼Fe:As 1: 1) than the amorphous precipitates (Fe:As >3: 1). These latter compounds consist mainly of amorphous ferrihydrite which on ageing can dehydrate and recrystallise and may release adsorbed arsenic due to reductions in surface area and active sites. Therefore the formation of stable crystalline compounds may be a more attractive disposal option for arsenic.