Removal of Sb(V) from textile wastewater with iron-based coagulants: Influence factors, precipitate speciation and mechanism analysis

The widespread use of antimony as a catalyst in the textile industry presents risks to ecosystems and human health. This study investigated the removal of Sb(V) using three iron-based coagulants —polymeric ferric sulfate (PFS), ferric chloride (FeCl 3 ), and ferrous sulfate (FeSO 4 )—via coagulation-sedimentation, and elucidates the coagulation mechanism by speciation analysis and characterization of precipitate. At a wastewater pH of 5–6, PFS and FeCl 3 achieved 96 % removal of 1.0 mg-Sb/L with a dosage of 12 mg-Fe/L, while FeSO 4 showed only 78 % removal, primarily due to the requisite oxidation step to Fe(III) before hydrolysis and precipitation. Phosphate ions, organic dyes and humic acids could compete with Sb(V), thereby reducing its removal efficiency. Sequential chemical extraction and instrumental characterization analysis revealed that the primary components of the precipitate were FeSbO 4 and Fe r SbO 4 (OH) 3r-3 when PFS or FeCl 3 was used as the coagulant. During Sb(V) removal process employing FeSO 4 coagulant, a large portion of Fe(II) underwent direct reaction with Sb(V) to form FeSb 2 O 6 , while the remaining fraction was oxidized to Fe(III) and generated FeSb 2 O 6 and Fe r SbO 4 (OH) 3r-3 via the Fe(III) reaction pathway. The removal of Sb(V) was mainly due to chemical precipitation (90 %) and hydrolysis adsorption (10 %). PFS coagulation is a promising method for removing Sb(V) from textile wastewater.