Abstract
Abandoned lead and zinc (Pb-Zn) mines around the world produce large amounts of acid mine drainage (AMD) containing Pb(II), which is toxic and accumulates in the environment and in living organisms. Bentonite-steel slag composite particles (BSC) are a new type of acid mine drainage (AMD) treatment material that can remove heavy metal ions and reduce acidity. To date, there have been no reports on the treatment of Pb(II)-containing AMD using BSC. Therefore, the effects of pH, reaction time, temperature, and Pb(II) concentration on the adsorption of Pb(II) onto BSC were studied. Moreover, the BSC before and after the reaction, as well as the precipitation after the reaction, were characterized by scanning electron microscopy and X-ray diffraction analyses. The effect of pH on the adsorption process is similar to that of the formation of soluble and insoluble hydrolysates of Pb(II) on pH. The adsorption mechanism includes ion exchange, complexation, precipitation, and synergistic adsorption–coagulation effect. Adsorption kinetics are best-fit with the pseudo-second order kinetics model ( R 2 > 0.98). Furthermore, the total adsorption rate is controlled by liquid film diffusion and in-particle diffusion, the liquid film diffusion rate being higher than the in-particle diffusion rate. The isothermal adsorption of Pb(II) onto BSC fit well with Langmuir and Brunauer Emmett Teller (BET) isotherms ( R 2 > 0.995), and both single layer adsorption and local multilayer adsorption were observed. Thermodynamic analysis revealed that the adsorption process is spontaneous and endothermic, and that the degree of freedom increases with time. In summary, this study provides a theoretical basis for the use of BSC in treating AMD containing Pb(II).
Highlights
Acid mine drainage (AMD) is an inevitable by-product of mining production in the case of the occurrence of sulfide minerals [1,2]
Our research group developed a new adsorbent named bentonite–steel slag composite particles (BSC) [34]. These particles benefit from the excellent adsorption potential of bentonite for heavy metal cations and the ability of steel slag to release alkalinity, which neutralizes acid, thereby precipitating heavy metal ions
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Summary
Acid mine drainage (AMD) is an inevitable by-product of mining production in the case of the occurrence of sulfide minerals [1,2]. Our research group developed a new adsorbent named bentonite–steel slag composite particles (BSC) [34] These particles benefit from the excellent adsorption potential of bentonite for heavy metal cations and the ability of steel slag to release alkalinity, which neutralizes acid, thereby precipitating heavy metal ions. These composite particles induce a synergistic adsorption–coagulation effect that aids the removal of heavy metal ions. Yuan et al prepared Fe2O3-ceramicite (FOC) by sintering bentonite, iron powder (IP), and activated carbon (AC) at 1073 K, which has a good adsorption properties for Pb(II) in AMD [36] Most of these reported adsorbents only have the function of removing Pb(II) and cannot neutralize AMD acidity. We studied in Sustainability 2019, 11, 4476 detail the removal behavior, influencing factors and removal mechanism of Pb(II) in AMD by a new adsorbent BSC, providing a theoretical basis for the treatment of Pb(II)-containing AMD by using BSC
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