Experimental Study on the Optimum Preparation of Bentonite–Steel Slag Composite Particles

Abstract

Novel multifunctional adsorbent bentonite-steel slag composite particles (BSC) were developed for highly efficient and synergistic treatment of heavy metal ions in acid mine drainage (AMD). Single-factor experiments were performed to examine the influence of different parameters on the adsorption effect, alkalinity release quantity, and loss rate of the composite particles. Based on these results, an L9(4 3 ) orthogonal experiment was carried out, and the optimum levels and order of the factors were determined by range analysis. Finally, the optimum preparation process of the composite particles was determined: a bentonite-steel slag proportion of 5:5, Na 2 CO 3 content of 5%, aging time of 12 h, calcination particle size of 2 mm, calcination temperature of 500 • C, and calcination time of 60 min. The isothermal adsorption of optimum BSC fit well with Langmuir and Brunauer-Emmett-Teller (BET) isotherms (R 2 R 2 > 0.997). A synergistic adsorption-coagulation effect occurs, leading to the appearance of multiple layers locally on the surface of BSC, which satisfies the BET model. To understand the preparation mechanism of the BSC, bentonite, steel slag, uncalcined BSC, and the optimum BSC were characterized using scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, X-ray powder diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The results indicate that calcination led to an increase in the average pore radius, total pore volume, and specific surface area (S BET ) in the optimum BSC; numerous pores were present on its layered surface. Although the layer spacing increased after calcination, the structure of the dioctahedra remained unchanged. Exchangeable Na + , montmorillonite, and alkaline components were present between the optimum BSC layers. Water and impurities were removed after calcination. The BSC not only released an alkalinity-neutralising acid but also induced a synergistic adsorption-coagulation effect that removed heavy metal ions. It is an excellent multifunctional protective material for the mining environment, that can treat AMD-containing heavy metal ions. Sustainability 2020, 12, 18 2 of 27 Current techniques for treating AMD containing heavy metals include the neutralization precipitation [11], electrochemical [12], membrane separation [13-15], microbial [16,17], constructed wetland [18], and adsorption [19,20] methods. Neutralization precipitation and adsorption are widely used [21,22]. However, neutralization precipitation requires a large amount of chemical agents, such as neutralizer and flocculent [23,24], which leads to difficulties in solid-liquid separation and high processing costs [25,26]. Besides various adsorbent materials, activated carbon is frequently used for adsorption, but has a low adsorption capacity for heavy metal ions, has high costs, and cannot neutralize acid [27][28][29]. At present, most treatments use a single method, and the treatment effect is poor. If two methods are connected in series, the process flow is long,...

Formation mechanism of carbide slag composite sustained-alkalinity-release particles for the source control of acid mine drainage

“…7 ). This decrease indicates that the mechanical strength of uncalcined particles is poor, and an excessive loss rate leads to the removal of Cu 2+ , which is consistent with the research results of Zhan 38 . However, an excessive loss rate leads to an increase in effluent turbidity and sludge.…”

“…The mass loss of particles during wastewater treatment is mainly caused by hydraulic shear, collision and friction between particles and/or between particles and container walls 36 . Therefore, the loss rate was used to characterize the mechanical strength of the particles, which to some extent match the breakage mechanisms in practical use of wastewater treatment 37 , 38 . The specific operation involved adding a consistent mass of particles to a 250 mL conical flask, adding 100 mL distilled water, and placing the flask in a shaker at 100 rpm for 12 h. Then, the particles were dried at 105 °C for 2 h, cooled at room temperature and passed through a 0.5 mm mesh sieve.…”

“…The specific operation involved adding a consistent mass of particles to a 250 mL conical flask, adding 100 mL distilled water, and placing the flask in a shaker at 100 rpm for 12 h. Then, the particles were dried at 105 °C for 2 h, cooled at room temperature and passed through a 0.5 mm mesh sieve. The remaining particles were weighed, and the loss rate was calculated as follows 38 : where ρ is the loss rate of composite particles (%), m 1 is the initial mass of composite particles (g), and m 2 is the mass of the composite particles after drying (g). The larger the loss rate is, the worse the mechanical strength of the particle.…”

Eco-friendly Nano-adsorbents for Pollutant Removal from Wastewaters

“…The relatively advanced technologies for wastewater treatment are required to increase pollutant destruction, for example, advanced oxidation methods (catalytic or photo-catalytic oxidation), electrocoagulation, adsorption, etc. [8]. These technologies allow removing pollutants that are impossible to remove by conventional methods, for example, heavy metals, organic compounds, suspended colloidal solids, nutrients, microorganisms, etc.…”