Investigation of the Effect of Mixed Anion and Mixed Metal on Heavy Metal Removal from Contaminated Aqueous Solutions

Aims: To investigate the effect of variation of metals (Cu vs Zn) and anions (nitrate vs sulfate) in heavy metal remediation by charcoal and coffee waste from contaminated water.

Study Design: Aqueous solution of single and mixed nitrate and sulfate salts of copper and zinc were respectively treated with charcoal and coffee waste for 12 hr and the residual metal concentration and percent metal removal were determined.

Place and Duration of Study: The experiments were conducted in the Chemistry Department at Dillard University between January 2021 and November 2021

Methodology: Coffee waste (2 grams) and charcoal (2 grams) were respectively mixed with 40 ml of 500 parts per million (ppm) of each of the following combination of metal solutions: Cu(NO3)2; CuSO4; Zn(NO3)2; ZnSO4; Cu(NO3)2 and Zn(NO3)2; CuSO4 and ZnSO4; Zn(NO3)2 and ZnSO4; Cu(NO3)2 and CuSO4; Cu(NO3)2 and ZnSO4; Zn(NO3)2 and CuSO4. Each solution was agitated for 12 hours at room temperature. The mixtures were centrifuged at 3000 rpm for 10 minutes and residual copper and zinc were analyzed. The results showed that copper was preferentially adsorbed by coffee waste compared to zinc in all binary metal (copper-zinc) solutions. Copper removal by coffee waste from CuSO4 and CuSO4-ZnSO4 were 43.9% and 65.5% respectively. Zinc removal from ZnSO4 and CuSO4-ZnSO4 by coffee waste was 34.79% and 20.3% respectively. Conversely, the zinc removal from mixed copper-zinc salt solutions, CuSO4-ZnSO4 and Cu(NO3)2-Zn(NO3)2 were 70.5% and 79.9% respectively.

Conclusion: Metal type can affect the extent of metal removal from mixed metal solutions. In this research, the copper was 21% more effectively removed from the mixed metal solutions than from a single metal-single anion solutions. In addition, zinc removal was11-14% suppressed in binary metal salt solutions compared to its removal from single-metal-single anion salt solutions. The anion type does not influence metal removed from single metal-single anion salt solutions. However, in the mixed metal-mixed anion systems, more metals were removed when the anion is a nitrate than when it is a sulfate, especially with coffee waste as adsorbent. 9.4% more zinc was removed from CuSO4-Zn(NO3)2,79.9%) than from ZnSO4-Cu(NO3)2, 70.5%). Thus, both metal and anion type affect extent of metal removal from mixed metal mixed anion.