Effect of Bioprecipitation and Ferrochrome Ash Stabilization on the Strength of Black Cotton Soil

Abstract

This study aims to stabilize black cotton soil in an environmentally friendly manner by integrating chemical stabilization and bioprecipitation. To improve the unconfined compressive strength (UCS), the soil was partially replaced by ferrochrome ash (FCA) and blended with urease positive bacteria, urea, and calcium chloride. Characterization studies examined microstructural changes. Leachate analysis determined whether this method is environmentally safe. Consequently, experiments were conducted using a central composite design and the UCS was modeled using response surface methodology (RSM) to evaluate the influence of each additive. Liquid extracts of stabilized soil were analyzed for concentrations of chromium, iron, zinc, lead, nickel, cadmium, copper, titanium, mercury, and arsenic. An improvement in the UCS from 35 kPa to 350 kPa was noticed when 40% of the soil was replaced with FCA and mixed with a bacterial solution of optical density 1.12, containing 0.5 g calcium chloride and 0.5 g urea. FCA content, the optical density of the bacteria, and the urea concentration were the factors affecting the UCS significantly. Lead, cadmium, titanium, mercury, and arsenic were not detected in water-based extracts of stabilized soil due to the immobilization effect of calcite. X-ray diffraction (XRD), Field emission gun scanning electron microscopy (FEGSEM), Fourier transform infrared spectroscopy (FTIR), and Thermogravimetric (TG) analyses supported the formation of calcite due to bioprecipitation. Based on the results, it is concluded that FCA and bioprecipitation complement each other to overcome their limitations and successfully enhanced the strength of black cotton soil in an environmentally conscious manner. © 2023, The Author(s), under exclusive licence to Springer Nature Switzerland AG.