Enhancing the effect of zinc oxide on the absorption of heavy metals from wastewater by using silica in graphene bed

In this study, the effects of nanostructure absorbent of zinc oxide (ZnO) in graphene bed for wastewater treatment were studied. Initial analysis was undertaken to identify the existing metals and their concentration in the prepared wastewater. It was seen that the diluted solution consisted of the ambivalence ions of lead, copper, nickel, cadmium, and silver with the concentration of 73.31, 81.19, 54.6, 98.1and 76.1 milligram per liter, respectively. Trivalent chrome, with a concentration of 98.1 milligram per liter was also observed. Therefore, by adding various amounts of absorbent (20, 30 and 50 mg) to the wastewater sample and adjusting the pH to 5 and 6, each metal was separately absorbed. Consequently, the concentration of the remaining metals was measured, and it was observed that absorbent was effective for the absorption of lead, copper and silver (with a reduction of up to 80%), however, the absorbent was weak in the absorption of nickel and chrome. Hence, the silicon nanoparticles added to absorbent and the experiments repeated. It was observed that the presence of silicone resulted in higher absorption of nickel and chrome but negatively affected the absorption of copper and silver. Electrical charges at lower pH’s have an inverse impact on the absorption of metal ions that is due to the electrostatic repelling forces between the positive charges. In more acidic solutions, the carbonyl groups in the surface of composite create positive charges and hence repel the metal ions. Hence, the performance of the absorbent improves by reducing the acidity of the solution. At the pH of six, the number of hydroxide increases and the capacity of absorbing metal cations increase.