Evaluation of removal performance of hexavalent chromium species using montmorillonite clay and iron coagulant

Abstract

Chromium ion contamination in surface and groundwater is a pressing global issue that demands urgent improvements in treatment systems to lower toxic levels. In accordance, conventional water treatment processes like coagulation, flocculation, and sedimentation (C/F/S) offer practical pathways to ensure public safety. Therefore, in current research, single and combined effect of ferric chloride (FC) coagulant and montmorillonite clay for hexavalent chromium (Cr(VI)) removal from water was examined. The results indicated greater Cr(VI) removal performance of FC coagulant (93.9% at a dosage of 0.12 g/L) at pH 5 than montmorillonite clay (13.27%, at 0.1 g/L) and combined system with 0.12 g/L FC and 0.1 g/L montmorillonite clay (84.3%). Maximum Cr(VI) removal was observed in acidic conditions (93.49% at pH 4) while removal potential of FC coagulant continuously decreased with increase in pH (64.31% at pH 6, 49.57% at pH 7, 36.34% at pH 8 and 28.71% at pH 9). Single and combined interfering ions effects were evaluated where results showed maximum Cr(VI) removal of 87.97% in presence of chloride and minimum Cr(VI) removal of 52.52% in presence of phosphate, while in presence of mixture of interfering ions, 64% Cr(VI) removal was observed. Moreover, turbidity removal was also monitored before and after FC coagulation, with results showing a significant decline in turbidity from (41.4 NTU to 492 NTU) to below 0.01 NTU, thus showing excellent coagulation performance. Sorption data showed better fitting with the Freundlich model (R2: 0.92), indicated multilayer Cr (VI) adsorption on heterogeneous sites of the FC coagulant, surpassing the Langmuir model (R2: 0.85). In general, this research underscores the promising application and usage of FC coagulant in removing particulates as well as dissolved metal ions from aqueous solutions, thereby providing critical insights to drinking water treatment industries. Keywords: Hexavalent chromium removal, ferric chloride coagulant ,montmorillnite clay, coagulation/flocculation/sedimentation,water treatment.