Removal of lead and cadmium from aqueous solutions by using 4-amino-3-hydroxynaphthalene sulfonic acid-doped polypyrrole films

Abstract

Water pollution by heavy metals is a great health concern worldwide. Lead and cadmium are among the most toxic heavy metals because they are dangerous for the human and aquatic lives. In this work, the removal of lead and cadmium from aqueous solutions has been studied using electrosynthesized 4-amino-3-hydroxynaphthalene-1-sulfonic acid-doped polypyrrole (AHNSA-PPy) films as a new adsorbent. Two distinct methods, including the immersion method, based on the Pb²⁺ and Cd²⁺ spontaneous removal by impregnation of the polymer in the solution, and the electro-elimination method, consisting of removal of Pb²⁺ and Cd²⁺ ions from the solution by applying a small electrical current (5 mA) to the polymer film, were developed: the evolution of Pb²⁺ and Cd²⁺ concentrations with time was monitored by inductively coupled plasma optical emission spectrometry (ICP-OES). The effect of pH on the adsorption and electro-elimination of Pb²⁺ and Cd²⁺ using the AHNSA-PPy film was investigated and optimized, showing that the ionic adsorption and electro-elimination processes were highly pH-dependent. The kinetics of Pb²⁺ and Cd²⁺ adsorption and electro-elimination were found to follow second-order curves. The maximum adsorption capacity values of the AHNSA-PPy film were 64.0 and 50.4 mg/g, respectively, for Pb²⁺ and Cd²⁺. The removal efficiency values were, respectively, for Pb²⁺ and Cd²⁺, 80 and 63% by the immersion method, and 93 and 85% by the electro-elimination method. Application of both methods to Senegal natural waters, fortified with Pb²⁺ and Cd²⁺, led to removal efficiency values of, respectively for Pb²⁺ and Cd²⁺, 76–77 and 58–59% by the immersion method, and of 82–90 and 80–83%, by the electro-elimination method.