Removal of Lead Ions from Aqueous Media Using Rice Husk Modified with Manganese Oxide

Abstract

The creation of effective adsorbents from agricultural waste to remove heavy metals such as toxic lead ions has been widely used. The goal of this research is to remove lead from water using rice husk-manganese oxide (RH-Mn). The raw rice husk was processed in three stages: (1) treatment with hydrochloric acid (HCl) 1M and sodium hydroxide (NaOH) 1M; (2) keep treating the material at the first stage in an ultrasonic water bath with a solution of 50 mL distilled water and 5 mL ethanol (90°C) plus 1,5g potassium permanganate (KMnO4); (3) Continuously adding few drops of 10% hydro peroxide (H2O2) to the solution and stirring until the precipitation solid turns brown or black. The material was filtered and dried for 6 hours at 800C. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) were used to determine MnO2 and observe the differences between the raw rice husk and modified rice husk. Besides, batch adsorption tests were carried out to investigate the influence of time, pH, and adsorbent dose on the adsorption removal process. Particularly, several outstanding performances in the research are: (1) Based on the statistically experimental design and response surface method (RSM) were applied to improve the adsorption system; (2) Pseudo-second-order kinetics and Freundlich isotherm models were shown to be effective in explaining lead adsorption on RH-Mn; (3) The modified adsorbent took four hours to reach the adsorption equilibrium. Over 99% of lead ions were eliminated from water under ideal conditions if the pH of the water was 4, the initial concentration was 15 mg/L, the contact period was 3 hours, and the RH-Mn dose was 1.5 g/L. This research can aid in the development of novel bioengineered low-cost adsorbents.