Abstract
Soil treatment methods to cope with ever-growing demands of construction industry and environmental aspects are always explored for their suitability in different in-situ conditions. Of late, enzyme induced calcite precipitation (EICP) is gaining importance as a reliable technique to improve soil properties and for contaminant remediation scenarios. In the present work, swelling and permeability characteristics of two native Indian cohesive soils (Black and Red) are explored. Experiments on the sorption and desorption of multiple heavy metals (Cd, Ni and Pb) onto these soils were conducted to understand the sorptive response of the heavy metals. To improve the heavy metal retention capacity and enhance swelling and permeability characteristics, the selected soils were treated with different enzyme solutions. The results revealed that EICP technique could immobilize the heavy metals in selected soils to a significant level and reduce the swelling and permeability. This technique is contaminant selective and performance varies with the nature and type of heavy metal used. Citric acid (C6H8O7) and ethylene diamine tetra-acetic acid (EDTA) were used as extractants in the present study to study the desorption response of heavy metals for different EICP conditions. The results indicate that calcium carbonate (CaCO3) precipitate deposited in the voids of soil has the innate potential in reducing the permeability of soil up to 47-fold and swelling pressure by 4-fold at the end of 21 days of curing period. Reduction in permeability and swell, following EICP treatment can be maintained with one time rinsing of the treated soil in water to avoid dissolution of precipitated CaCO3. Outcomes of this study have revealed that EICP technique can be adopted on selected native soils to reduce swelling and permeability characteristics followed by enhanced contaminant remediation enabling their potential as excellent landfill liner materials.
Highlights
Effect of toxic heavy metals on the environment has become a serious concern to the entire world because of the intrusion of heavy metals in the ecosystem [1]
Sorption of Cd dominated Ni in raw soil, that is 2.0968 mg/g of Cd and 1.8862 mg/g of Ni was sorbed on the raw red soil sample and the solution pH was 6.21 whereas 4.8215 mg/g and 4.3166 mg/g Cd and Ni respectively were sorbed on red soil treated by E2 while the pH was 7.11 both the results shown here are of initial concentration of 100 mg/L
Permeability and Swell Behavior of Soils. It was observed from the results obtained that the coefficient of permeability (K) of the untreated red soil was 5.3 × 10−7 cm/s and for red soil treated with E2, K reduced to 1.12 × 10−10 cm/s after a curing period of 21 days
Summary
Effect of toxic heavy metals on the environment has become a serious concern to the entire world because of the intrusion of heavy metals in the ecosystem [1]. Heavy metals cannot be decomposed and extirpated from the ecosystem because of their stability and cause atrocious health issues to the aquatic and terrestrial life [2]. Soil pollution due to heavy metals has become a grave concern to be addressed [3] since it poses threat to the food security of the world [4], and it is not just hazardous to living creatures but it is a worldwide environmental issue [5,6]. Cause heavy metal pollution in the environment [7]. The scale to which the heavy metal pollution has increased makes it imperative to find for the remediation methods. One of the methods of heavy metal remediation in the soils is immobilization by solidifying the soil by a binder, which reduces the activity and solubility of heavy metals and even improves the mechanical characteristics of soils [10,11]
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