Effects of nitrate and Fe/As molar ratio on direct iron(III)-arsenite precipitation in high-sulfate–chloride wastewaters

The addition of an arsenite-chloride solution into an arsenite-sulfate solution is extremely beneficial for the removal of As(III) via Fe(III) salt precipitation at pH 2.3. However, the applicability of this method to complicated high-As(III) metallurgical wastewaters still requires further verifica...

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Published in:	Environmental science and pollution research international 2023-03, Vol.30 (14), p.40230-40241
Main Authors:	Yuan, Zidan, Zhao, Xiaoming, Yang, Liqiong, Wang, Shaofeng, Lin, Jinru, Jia, Yongfeng
Format:	Article
Language:	eng
Subjects:	Aquatic Pollution Arsenite Arsenites - analysis Atmospheric Protection/Air Quality Control/Air Pollution Chemical precipitation Chloride Chlorides Complexation Earth and Environmental Science Ecotoxicology Environment Environmental Chemistry Environmental Health Environmental science Ferric Compounds - chemistry Immobilization Iron Iron - chemistry Metal industry wastewaters Metallurgy Nitrates Oxidation-Reduction Research Article Sulfates Sulfur Oxides Synergistic effect Waste Water Technology Wastewater Water Management Water Pollution Control
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Summary:	The addition of an arsenite-chloride solution into an arsenite-sulfate solution is extremely beneficial for the removal of As(III) via Fe(III) salt precipitation at pH 2.3. However, the applicability of this method to complicated high-As(III) metallurgical wastewaters still requires further verification. This work investigated the effects of nitrate and Fe/As molar ratio on As(III) immobilization using Fe(III) in three acid radical media including sulfate, chloride, and nitrate at pH 2.3. Our results indicated that 72.1‒93.5% of As(III) was precipitated, which was 5‒10% less than those obtained in the nitrate-free systems. The Fe/As molar ratio of 4 was the optimal condition with an average of 93% As(III) removal based on a broad sulfate/chloride molar ratio range (1:1‒16). However, a maximum of 96% As(III) removal was observed under the Fe/As molar ratio of 1.5 and the sulfate/chloride condition of 1:16. The negative correlation between complexation and precipitation was attributed to the enhanced initial complexation by the synergistic effect of the mononitratoiron complex and FeH 2 AsO 3 2+ . The variation of Fe/As molar ratios resulted in the diverse solid species, thus further affecting the As(III) removal efficiency. Despite producing tooeleite as a major As(III) host phase, ferrihydrite and poorly crystalline ferric arsenite hydroxysulfate formed simultaneously at the Fe/As molar ratio of 4 participated in As(III) immobilization compared with the solid products at Fe/As molar ratios ≤ 2.
ISSN:	1614-7499 0944-1344 1614-7499