Abstract:

Schwertmannite is an iron hydroxyl sulfate secondary mineral which is commonly found in acid mine drainage (AMD). It can stowage the heavy metals in AMD by means of isomorphic replacement. However, schwertmannite with different Fe-S ratios may show different surface properties and characteristics, thus affecting their applications in environmental treatments or remediations. In this paper, schwertmannite with different Fe-S ratios were synthesized by a rapid chemical method combined with sodium sulfate regulation, and the effects of Fe-S ratios on the microstructure of schwertmannite were investigated by XRD, BET, FTIR, SEM and TEM. On this basis, the differences in the adsorption capacity of schwertmannite for Cr(Ⅵ) were explored, as well as the elucidation of the mechanism about chromium adsorption and its influencing patterns. The result showed that there was no obvious difference in the crystal form of schwertmannite with different Fe-S ratios ranged from 4.70 to 6.20. But the crystallinity of schwertmannite increased as the sulfate content elevated. SEM and TEM results suggested that the minerals appeared to be spherical particles and packed densely with a few granular burrs on the surface, of which the specific surface area followed the order of Sch 1 > Sch 2 > Sch 5 > Sch 4 > Sch 3. Batch adsorption experiment results revealed that under the same experimental conditions, the best Cr(Ⅵ) adsorption efficiency which achieved 85.6% was found in the schwertmannite with a Fe-S ratio of 5.32 when the pH was 5.00 and the initial concentration of Cr was 5 mg?L^-1. The XRD results showed that Sch 1 showed a trend of transitioning to goethite after the adsorption of Cr(Ⅵ), while the crystallinity of other schwertmannite was basically unchanged after the reaction. The correlation between the adsorption of CrO₄^2- and the structure SO₄^2- was proved by the characterization of FTIR, which implied that the adsorption process of Cr(Ⅵ) by schwertmannite involved the ion displacement reaction of sulfate ligand exchange. Therefore, different Fe-S ratios will affect the microstructure of schwertmannite, and an appropriate Fe-S ratio (5.32) was conducive to the adsorption of Cr(Ⅵ). In addition, attention should be paid to the environmental conditions to prevent schwertmannite from destabilization. Results of this study could provide a theoretical basis and evidence for the remediation of chromium and application of schwertmannite in the field of environmental remediation.

Key words: schwertmannite, chromium, Fe-S ratio, adsorption

摘要：

施氏矿物是酸性矿山废水（AMD）中常见的铁羟基硫酸盐次生矿物，可通过类质同象置换对AMD中重（类）金属起到固载作用，但不同Fe-S比率的施氏矿物可能会呈现不同的表面性质和特征，进而影响着其在环境治理与修复中的应用。采用快速化学法结合硫酸钠调控合成制备不同Fe-S比率的施氏矿物，并通过XRD、BET、FTIR、SEM和TEM等表征手段探究了Fe-S比率对施氏矿物微观结构的影响，在此基础上探索施氏矿物对六价铬吸附的差异性能，并初步阐明施氏矿物吸附铬的作用机理及其影响规律。结果表明：所合成的5种施氏矿物Fe-S比率范围为4.70－6.20，不同Fe-S比率的施氏矿物晶型无明显差异，但矿物中硫酸盐含量越高会导致矿物的结晶度增加，SEM和TEM表明矿物呈现堆叠的球状颗粒，表面有少量小颗粒毛刺，比表面积大小遵循Sch 1>Sch 5>Sch 2>Sch 4>Sch 3。批吸附实验结果表明在相同的实验条件下，Fe-S比率为5.32的施氏矿物对Cr(Ⅵ)的吸附效果最佳，当pH为5.00和Cr的初始质量浓度为5 mg?L^-1时，其去除率为85.6%。XRD结果显示Sch 1的环境稳定性最差，反应后呈现向针铁矿转变的趋势，而其它施氏矿物反应后晶型基本不变。FTIR表征结果证明CrO₄^2-的吸附与结构SO₄^2-之间的相关性，揭示了施氏矿物对Cr(Ⅵ)的吸附过程涉及SO₄^2-产生配位体交换的离子置换反应。因此，不同的Fe-S比率会影响施氏矿物的微观结构，适当的Fe-S比率（5.32）有利于施氏矿物对六价铬的吸附，另外应关注环境条件，防止施氏矿物失稳。研究结果可为环境中铬的治理及施氏矿物在环境修复领域中的应用提供理论依据和数据支撑。

关键词: 施氏矿物, 铬, Fe-S比率, 吸附