Corn Cob-Derived Activated Carbons for Gold Mine Wastewater Treatment in East Cameroon

In East Cameroon, the discharge of untreated effluents, from gold recovery and concentration, into nature poses serious environmental problems. The main aim of this study was to investigate the efficiency of three corn cob-derived activated carbons for gold mine wastewater treatment of East Cameroon. Wastewater samples were collected in three mining sites (Kambele 1, Kambele 2 and Dem) for laboratory analysis. The three activated carbons were produced by chemical and thermal activation with three different chemical reagents (ZnCl<sub>2</sub>, NaOH, and KH<sub>2</sub>PO<sub>4</sub>, respectively) meanwhile Al<sub>2</sub>(SO<sub>4</sub>)<sub>3 </sub>served as the control. The main results revealed that wastewater from Kambele 2 area was the most contaminated with highest proportion of Fe (3.52 mg/l), Hg (62.7 mg/l), Cd (533.95 mg/l), NO<sub>3</sub><sup>-</sup> (103.33 mg/l), SO<sub>4</sub><sup>2-</sup> (640 mg/l), HCO<sub>3</sub><sup>- </sup>(152.5 mg/l), Ca<sup>2+</sup>(447.12 mg/l), Na<sup>+</sup> (26.8 mg/l), Mg<sup>2+</sup> (32 mg/l), K<sup>+</sup> (51.05 mg/l). And with low proportion of Ni (0.21 mg/l), Pb (0.41 mg/l), PO<sub>4 </sub>(0 mg/l), and Mn (5.66 mg/l), as compared to wastewater from the other sites. Wastewater samples from this site were used to test the efficient of ACs. The wastewater was greatly improved with ACZnCl<sub>2</sub> and ACNaOH, but ACNaOH performed better than the control and other activated carbons for cationic extraction, and was the only AC to adsorb almost 100 % of Hg in wastewater. The ACZnCl<sub>2</sub> (0.5 mm particle size) was the most efficient in the extraction of major anions: NO<sub>3</sub><sup>-</sup> (96.60 %), SO<sub>4</sub><sup>2-</sup> (81.25 %), HCO<sub>3</sub><sup>-</sup> (76 %), compared to the Ca(OH)<sub>2</sub> and Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> (control) and ACNaOH. Generally, the ACZnCl<sub>2</sub> (0.5 mm particle size) was more efficient compared to ACKH<sub>2</sub>PO<sub>4</sub> and ACNaOH in adsorption of Fe (94.05 %), Mn (88.51 %), and Ni (99.99 %). The Al<sub>2</sub>(SO<sub>4</sub>)<sub>3 </sub>was the only one that reduced the concentration of Pb (24.39 %) and was good for extraction of NO<sub>3</sub><sup>-</sup> (96.6 %), Fe (92.6 %), Mn (88.51 %), and Ni (99.99 %). From ACZnCl<sub>2</sub>, the smaller the particle size of cob-derived AC, the better the extraction of heavy metals and anions and the poorer the extraction of cations (Ca<sup>2+</sup>, Na<sup>+</sup>, Mg<sup>2+</sup>, K<sup>+</sup>). The economic analysis of the different methods enabled to note an additional profit rate of 60 to 160% with the use of the ACs compared to Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>. Thus, ACZnCl<sub>2</sub> and ACNaOH can either be used alone or combined with Al<sub>2</sub>(SO<sub>4</sub>)<sub>3 </sub>for best performance to reduce cost and optimize contaminant removal.