Removal of heavy metal ions from wastewater by combined modified kaolin

The removal of lead Pb (II) and cadmium Cd (II) from wastewater by using three different types of kaolin including natural kaolin, sodium hydroxide NaOH-modified kaolin, and NaOH-calcination-modified (combined modified) kaolin was studied. Textural properties of the three types of kaolins were characterized by scanning electron microscopy, fourier transform infrared spectroscopy, and specific surface area analysis. The effects of calcination temperature, contact time, adsorption temperature, pH, and kaolin dosage were investigated. Results showed that NaOH-calcination-modified kaolin performed best among the three kaolins in removing Pb (II) and Cd (II). Compared to NaOH-modified and natural kaolin, the shape of combined modified kaolin was irregular, and its surface was rough and loose with bigger pore volume. The adsorption capacity of Pb (II) and Cd (II) could reach the maximum of 161.84 and 108.13 mg g(-1) respectively, under the following condition: initial concentration of heavy metals ions was 200 mg L-1, pH was 5.5, adsorption temperature was 25 degrees C, contact time was 60 min, and NaOH-calcination-modified kaolin dosage was 1 g. Combined modified kaolin was also applied to remove heavy metal ions from actual industrial wastewater samples, and the results demonstrated that modified kaolin is a type of useful adsorbent for the removal of heavy metals from wastewater. Furthermore, the adsorption process of kaolin on Pb (II) and Cd (II) conformed to first and second-order kinetics equation, respectively.