Study of surfactant interaction with soils contaminated by heavy metals using voltammetry

Abstract

The objectives of this study were to develop a method to assess the heavy metalsurfactant-soil interaction and to clean the contaminated soils by a surfactant-ligandsystem. Soil was taken from Trakya, Tekirdag region. The soil samples were artificiallypolluted by cadmium with different concentrations and V/m ratios (where V stands for thesolution volume added on the soil and m for the weight of soil taken) for 25 hours whichwas determined as the equilibrium time of the interaction between cadmium ions and soil. The artificially polluted soil by cadmium at various concentration levels were brought intocontact with anionic surfactant, SDS (Sodium dodecyl sulfate) for 25 hours on a shaker at atemperature of 25 ± 20C. The concentrations of SDS were set at critical micelleconcentration (CMC), below and above CMC level. The amount of remaining cadmium was determined by Differential Pulse Anodic Stripping Voltammetry (DPASV) with theoptimized method parameters of -1.10 V of deposition potential, 90 s of deposition time,and 2000 rpm of a stirring rate. Hanging Mercury Dropping Electrode (HMDE) was usedas the working electrode. It was concluded that with the increasing SDS concentration, the amount of desorbed cadmium from the soil increased.Preliminary experiments were done to optimize the heavy metal-ligand-surfactantsystem. Ethylenediamineteraaceticacid (EDTA) and metal interaction was studied underacidic, neutral and basic conditions but no reproducible results were obtained with DPASV. Therefore, another ligand ethylene diamine (EN) was used in combination with aphosphate buffer. Cd-EN peaks were reproducible but Cd-EN-SDS aqueous mixtureresulted in an emulsion formation. DPASV experiments showed that the Cd-EN complexwas not taken into SDS micelle. EN was a good ligand for cadmium complexation reactions. However, the optimized method parameters for DPASV was inadequate toverify the role of SDS for remediation approaches in the presence of EN.