The effect of using electrokinetic process on reducing the salinity of clay and sandy soils

Approximately ۲۰% of agricultural land and ۵۰% of cropland in the world is under stress of salinity [۱, ۲]. The overuse of fertilizers and inappropriate water management are two main reasons for that. A certain quantity of salts is essential for plant growth but an excess amount can have negative effect on that [۱, ۲]. In recent years, electrokinetic remediation was studied as a promising process to remove salts or other contaminations from soil with the least changes in soil texture [۳-۶].In an Electrokinetic remediation experiment, electrodes are installed in two sides of the soil field and an electrical gradient is applied across them. Electrolysis reactions are generated at the electrodes, producing H+ and OH-. In this method, contaminants are transported by three main mechanisms, including electromigration, electroosmotic advection of the pore fluid in the soil medium, and electrophoresis. Different factors affect the final removal result by this process including soil type which determines the behavior of the transport mechanisms [۷, ۸]. The aim of this study is to evaluate the effect of voltage gradient and soil type on the ability of electrokinetic process in decreasing soil salinity in two different level.In this regard, ۸ experiments were designed for two different soil types (clay and sandy), two levels of salinity (none-saline and moderately saline) and two voltage gradients of ۱ and ۲ V/cm applied for ۸ days. Sodium chloride was the major cause of the salinity in the artificially salinized soil.In electrokinetic setup, soil compartment was placed between electrode chambers and was filled with compacted soil. Soil moisture was ۱۵-۲۰% initially and ۲۰-۲۵% during the experiment. The electrode chambers were filled with distilled water and a graphite electrode was placed in each one. Electrolytes were refreshed daily. Blank experiments without applying voltage gradient were prepared to check the salinity removal by concentration gradient. During the experiment, soil samples were collected daily for salinity measurements. The Salinity of soil can be expressed in term of its electric conductivity (EC) measured by using a conductivity meter.Based on obtained results, the electric current in non-saline clay soil is higher than sandy soil in both applied voltages. This difference is negligible in the moderately saline soil (due to the presence of salt ions in large quantities and the increase in conductivity of the soil). Due to having finer particles with more contact points between them, clay soil has higher conductivity.Commonly in all experiments, on the second day of the process, we see an increase in EC of the soil. According to previous studies, this result, especially in the part near the anode, can be due to the accumulation of anions (here probably Cl-) in this part [۱]. In the continuation of the process, with the exit of these ions to the electrolyte, we face a decrease in EC. There was less accumulation at higher voltages which have led to rapid release of more ions into the anolyte, so the soil salinity has decreased more dramatically. In all cases, the electrokinetic process has reduced the salinity of the soil in a great extent and brought it close to the range of non-saline soil. Applying a higher voltage to the soil has led to a further decrease in electrical conductivity on the eighth day

کلیدواژه ها:

Electrokinetic ، Saline Soil ، Soil type ، Electromigration