Behavior and mechanism of efficient arsenic removal by arsenate double salt mineralization precipitation
In response to the challenge of inefficiency in selectively removing arsenic from alkaline arsenic containing wastewater using conventional chemical precipitation methods,a proposal was set forth to employ arsenate double salt mineralization precipitation for wastewater treatment.Thermodynamic calculations were conducted on the Mg2+-NH4+-AsO43--OH--H2O system at 25℃,investigating the influences of process parameters on arsenic removal effect.The study established a kinetic control mechanism for the arsenate double salt mineralization precipitation process,while exploring the impact of impurity ions on arsenic removal efficacy.The results indicate that pH significantly affects both arsenic removal effect and arsenic residue quality.Increasing the dosages of magnesium and ammonia salts can enhance arsenic removal to a certain extent,yet excessive magnesium salt usage diminishes arsenic grade of arsenic residue with escalating dosage.Augmenting magnesium salt dosage facilitates a reduction in the time required to reach equilibrium.The addition of impurity ions Ca2+,Fe3+,and SiO32-fosters the creation of novel compounds,which subsequently co-precipitate with arsenic,thereby enhancing the process of arsenic removal.However,the addition of PO43-establishes a competitive relationship between the formation of phosphate double salt and arsenate double salt,consequently inhibiting arsenic removal by arsenate double salt mineralization.
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