In this research, kaolinite was used to investigate the comparative adsorption of copper, lead, and zinc ions through batch control experiments and first principles calculations. Different adsorption conditions were considered as the effect of solution acidity, initial concentration of ions, and contact shaking time. The adsorption system isotherms and kinetic studies were better agreed with the Langmuir and pseudo-second-order kinetic models. They reached adsorption equilibrium within two hours and maximum adsorption capacities of Zn(II), Pb(II), and Cu(II) on kaolinite were 15.515, 61.523, and 44.659 mg/g, respectively. In addition, the microscopic adsorption changes of Zn(II), Pb(II), and Cu(II) on kaolinite were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy with energy dispersive X-ray spectroscopy. The results showed that Zn(II), Pb(II), and Cu(II) were most likely to be adsorbed on the kaolinite surface. Furthermore, the adsorption mechanism of [Zn(OH)]+, [Pb(OH)]+, and [Cu(OH)]+ on the kaolinite (001) surface was systematically studied through first-principles density functional calculations. The adsorption characteristics of different ions were evaluated by calculating the adsorption energy of the equilibrium adsorption configuration, state density, and electron density. The adsorption energy of [Zn(OH)]+, [Pb(OH)]+, and [Cu(OH)]+ were − 0.49,  − 1.17, and − 1.64 eV, respectively. The simulation results indicated that new hybrid orbitals were formed between the metal ions and O atoms on the kaolinite surface, with electron transfer occurring the adsorption processes. The charge transfer direction for [Pb(OH)]+ was opposite those for [Zn(OH)]+ and [Cu(OH)]+. [Zn(OH)]+ was more likely to form polydentate complexes with hydroxyl groups on the kaolinite surface than [Cu(OH)]+ and [Pb(OH)]+. This work further elucidated the interaction mechanism between the adsorption systems and provided fundamental theoretical support for the structural modification and optimization of kaolinite, such as increasing the layer spacing of kaolinite and introducing other active groups on its surface to improve the adsorption capacity of heavy metal ions in water treatment and soil remediation.

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It has been reviewed that the Cu, Fe, and Mn are harmful to our environment, it needs our consideration to recover the water which has been contaminated by these metals and as well as when released without being treated and recovered, it will be harmful to the land and the soil and can be unfriendly for our environment. Toxic mining waste is a problem of more serious concern for both industries and the government. Several copper tailings dumps have been abandoned and not sufficiently stabilized. Once the tailings containing toxic minerals and residual metals contact diluents like rainwater, it forms acid mine water that can leach metals into groundwater, rivers, and streams. The effect of the different HCl addition was investigated under a fixed S: L of 1:2. The leaching temperature was set to 40°C, and leaching occurred for 2h. As presented in Tables 1 & 2, the leaching efficiency of the metals increased gradually with an increasing amount of HCl. The AAS method showed the leaching efficiency of 0.03±0.01% and 0.04±0.02% for Cu with the addition of 1.5 and 2 mL/g of HCl. For Fe, leaching efficiencies of 17.38±3.55% and 15.94±2.41% were obtained with the addition of 1.5 and 2mL/g of HCl. However, 0.39±0.02% and 0.38±0.01% for Mn were leached when adding 1.5 and 2mL/g of HCl. Statistically, there was a non-significant (p<0.05) difference in the leaching efficiency of Cu, Fe, and Mn among the different concentrations of HCl. Using the XRF method, the leaching efficiency of 12.09±2.40% and 9.5±1.84% for Cu was obtained by adding 1.5 and 2mL/g of HCl. For Fe, leaching efficiencies of 1.5±0.11% and 1.35±0.05% were obtained with the addition of 1.5 and 2mL/g of HCl. However, 16.54±5.21% and 15±2.49% for Mn were leached when adding 1.5 and 2mL/g of HCl. Statistically, there was a non-significant (p<0.05) difference in the leaching efficiency of Cu, Fe, and Mn among the different concentrations of HCl. It is concluded that Cu, Fe, and Mn from the low-grade copper tailing are successfully recycled via H2SO4 leaching and subsequent fractional precipitation technology. Based on the mineral composition analysis results, leaching temperature, the amount of H2SO4 added, leaching time, and S:L have been evaluated for leaching efficiencies. The amount of H2SO4 added, and S:L have strongly influenced the leaching efficiency.

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