Acid mine drainage (AMD) has caused serious and long-lasting damage to the environment in many countries. Preventing AMD formation at the source is considered the most direct and effective method of remediation. Carbide slag, an industrial waste, is a potential AMD treatment material due to its strong alkalinity. However, applying carbide slag at the source carries difficulties due to its rapid release of alkalinity. This is the first attempt to mix carbide slag with bentonite to prepare sustained-alkalinity-release particles for source control of AMD. The size of Ca(OH)2 crystallites is decreased from 267 to 211 nm, and the reduced part forms calcium silicate hydrate gel (C–S–H) between the carbide slag and bentonite. C–S–H encapsulated on the surface of the carbide slag, increasing the mechanical strength of the particles, and achieving slow release of alkalinity. The suggested optimum preparation conditions for the particles are as follows: bentonite-to-carbide slag mass ratio of 3:7, Na2CO3 dose of 10 wt%, and calcination temperature of 500 °C for 1 h. The particles can remove 105 mg/g Cu2+ within 12 h, and the loss rate is only 7.4%. The alkalinity release time of the particles is 4 times greater than that of carbide slag.

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In order to study the removal efficiency of Cu 2+ from acid mine drainage by prepared bentonite-steel slag composite particles, adsorption experiment was carried out. The composite particles were characterized by X-ray Diffraction analysis technique (XRD), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared spectrometer (FTIR). The results show that: the composite particles can release alkali to neutralize the acid of acid mine drainage; the adsorption and chemical precipitation of Cu 2+ occurred in the whole reaction process; the removal amount of composite particles on Cu 2+ was 9.88 mg/g when the reaction reached equilibrium; the FTIR spectra revealed the existence of surface complexation; the SEM micrographs suggested that the composite particles would continue to adsorb and coagulate Cu 2+ after the composite particles surface adsorbing Cu 2+ and forming precipitate, namely, there was synergistic reaction of adsorption and coagulation; the XRD patterns further showed the existence of cation exchange and revealed that the states of Cu 2+ in the surface of the composite particles was Cu-Si-O mineral phase and CuO(Cu(OH)2) polymerization precipitation. The bentonite-steel slag composite particles which can play a role of adsorption-coagulation synergism are excellent multifunctional green environmental mineral materials to treat acid mine drainage containing heavy metal ions.

The Acid Mine Drainage has characteristics of low pH, high concentrations of heavy metal ions, such as Fe 2+ , Mn 2+ , Cu 2+ and Zn 2+. In this paper, the composite particles that consisted of bentonite and steel slags were used to dispose the Acid Mine Drainage. Bentonite is the mineral materials and can adsorb heavy metal ions excellently. The steel slags are alkaline and industrial solid waste for the treatment of the Acid Mine Drainage. The main influencing factors, such as adsorbent dosages, shaking rates, concentrations of heavy metal ions, temperatures, adsorption time and pH value were studied by the static experiment. Increasing the adsorbent dosages and the concentrations of the heavy metal ions, speeding up the shaking rates, raising the temperatures, extending the adsorption time and improving pH would improve the removal efficiencies of heavy metal ions. Through considering the removal efficiencies and the treatment costs, the optimum reaction conditions for the four kinds of heavy metal ions were obtained. The adsorbent dosage 21 mg/L, the rotational speed 120 r / min, the temperature 25℃ , adsorption time 100 min and the initial wastewater pH 7. The four kinds of heavy metal ions existed independently in the simulated mine wastewater. The highest initial concentrations of Fe 2+ , Mn 2+ , Cu 2+ and Zn 2+ were 150 mg/L, 100 mg/L, 170 mg/L and 140 mg/L respectively. The removal rates were 93.42%, 92.64%, 93.86% and 95.17% respectively. The determination of the particles' SEM-EDS Microscopic characterization showed the composite particles could play a part in neutralizing, absorbing and the chemical precipitation. The acidity decreased notably and the heavy metal ions of Fe 2+ , Mn 2+ , Cu 2+ and Zn 2+ were adsorbed and precipitated effectively. The research results can extend the practical engineering application of the composite particles.

Acid mine drainage is characterised by low pH and high concentrations of heavy metal ions, such as Fe . In this paper, composite particles consisting of bentonite and steel slags are used to dispose acid mine drainage. Bentonite is an mineral material which has an excellent capacity to adsorb heavy metal ions. Steel slags are alkaline, an industrial solid waste commonly used in the treatment of acid mine drainage. The main influencing factors, including adsorbent dosages, shaking rates, concentrations of heavy metal ions, temperature, adsorption time and pH value are examined using a static experiment. The results indicate that the removal efficiency of heavy metal ions improves when increasing the adsorbent dosages and the concentrations of the heavy metal ions, speeding up the shaking rates, raising temperature, extending the adsorption time and increasing pH value. With a consideration of removal efficiencies combining with treatment costs, the optimum reaction conditions for the four types of heavy metal ions are obtained, which are an adsorbent dosage of 21 mg/L, a rotational speed of 120 r/min, temperature 25℃, adsorption time 100 min and initial wastewater pH7. The highest initial concentration of Fe , Cu 2+ and Zn 2+ were adsorbed and precipitated effectively. The research results can extend the practical engineering application of the composite particles.