Experiments and geochemical modelling of arsenic interaction with clay-dominated soil from Rupnagar district of Punjab, India

Abstract

The present study investigates the interaction of the soil in Garhbaga village, located in the Rupnagar district of Punjab, India for As(V) adsorption under the influence of pH, contact time and varying arsenic concentrations. To understand the geochemical controls of arsenic mobilization in the region, batch sorption experiments were performed using soil obtained from arsenic contaminated district of Punjab. This study presents a novel approach by employing surface complexation models (SCMs) to investigate arsenic adsorption onto natural soils in the Punjab region, which has not been explored in previous literature. Furthermore, a comparison between Fe-based models, assuming ferrihydrite binding, and general composite (GC) approach, assuming adsorption on soil component surfaces, has not been conducted before, adding to the originality of this research. The adsorption kinetic experiment indicates about 70% adsorption of As(V) in about 4 h. The results of batch isotherm experiment shows that As(V) adsorption saturation onto the soil is reached at an aqueous concentration of about 0.89 mgL−1. The results of the pH edges study shows a maximum As(V) adsorption of 93.88% at a pH of 4. The Langmuir’s isotherm was the best fitted because the value of linear regression coefficient (R2 = 0.997) which verifies the monolayer adsorption of As(V). It was observed that the pseudo first order model best fitted for explaining the kinetic of As(V) adsorption onto the soil because it showed higher value of linear regression coefficient (R2 = 0.995). Further, three different diffused layer models under varied assumptions were used to capture the batch experimental results. The surface complexation model with general-composite (GC) approach fairly predicted the experimental results when compared to Fe-oxide based models. The GC model was able to capture the observed experimental results for adsorption isotherm and pH edges for the soil within reasonable RMSE of 6.22 % and 7.97 %, respectively.