Study On The Mechanism Of Sulfate Removal In Acid Mine Drainage Using Steel Slag

Based on the unique adsorption performance of steel slag and the current situation of acid mine wastewater treatment,this paper uses converter steel slag as adsorbent to treat acid mine wastewater,and focuses on the removal effect and mechanism of sulfate in wastewater.In order to further improve the adsorption efficiency of steel slag for sulfate in acid mine wastewater,magnesium ion was introduced to enhance sulfate removal based on steel slag treatment,and sulfate removal was verified using real acid mine wastewater.The main content of this article is as follows:（1）The performance analysis of experimental steel slag shows that there are mainly elements such as Ca,Fe,Si,Mg,and Mn in the steel slag,with the proportions of Ca and Fe atoms being 30.75%and 13.34%,respectively.The main phases of steel slag are Ca₂Si O₄,Ca Fe₃O₅,Ca O,Mg O,Fe₃O₄,Ca₃Si O₅,Ca CO₃,etc.The structure of steel slag is porous and the distribution of surface components is uneven;The functional groups on the surface of steel slag mainly include Si-O,CO₃^2-,Ca-O,O-H;The pore structure analysis shows that the steel slag has a layered aggregate mesoporous structure,with a specific surface area of 15.9625 m²/g,an average pore diameter of 11.8427 nm,and a pore volume of 0.03451 cm³/g;The results of toxicity leaching experiments show that the concentration of heavy metal ions in the leaching solution is lower than the detection limit specified in the"Identification Standard for Hazardous Wastes-Extraction Toxicity Identification GB-5085.3-2007",in which Cd,Ag,Be,Ba,As,Hg,and Se are not detected,that is,steel slag can be used as an adsorbent to treat acidic mine wastewater;（2）The removal efficiency of sulfate from acidic mine wastewater is affected by factors such as the solid-liquid ratio of steel slag,initial p H of the solution,particle size of steel slag,and initial sulfate concentration.The maximum removal efficiency and adsorption capacity were 79.15%and 36.79 mg/g,respectively.Mechanical analysis shows that sulfate removal is mainly achieved through neutralization precipitation,electrostatic attraction,and ligand exchange.Ca O and Ca（OH）₂in steel slag play a major role in the removal of sulfate from acidic mine wastewater,and sulfate is mainly deposited on the surface of steel slag in the form of Ca SO₄·2H₂O;High concentration of H⁺in wastewater can accelerate the dissolution of calcium-based components from steel slag,and cause some hydroxyl groups on the surface of steel slag to be protonated with positive charges.Under the action of electrostatic attraction,the negatively charged SO₄^2-is easily adsorbed and removed.The sulfate removal process conforms to the pseudo-second order kinetic model and the Freundlich isothermal adsorption model,indicating that there is chemical adsorption between steel slag and sulfate,which is mainly multi-layer adsorption,and the distribution of active sites in steel slag is uneven;The thermodynamic calculation results show that the sulfate removal from steel slag belongs to a spontaneous endothermic reaction;The adsorption of sulfate in acid mine wastewater by steel slag is chemical adsorption;Electrostatic attraction and ligand exchange are cooperatively completed;（3）After Mg²⁺ion strengthening,the adsorption amount and removal rate of sulfate efficiency increased from 11.07 mg/g and 17.33%to 49.65 mg/g and 77.30%,respectively,and the adsorption equilibrium time decreased from 5750 min to 360 min.The optimal parameters for the experiment are adsorption time 480 min,steel slag dosage 50 g/L,steel slag particle size<0.075 mm,initial solution p H=2,initial sulfate concentration 5000 mg/L,and Mg²⁺concentration 1000 mg/L.Mechanical analysis shows that adding Mg²⁺to the solution can improve the dissolution efficiency of Ca（OH）₂in steel slag,promote the increase of specific surface area and roughness of steel slag,and reduce the nucleation barrier of Ca SO₄·2H₂O;At the same time,in an alkaline environment,the formation of Mg（OH）₂particles in the solution provides the possibility for heterogeneous nucleation of Ca SO₄·2H₂O crystals.Mg²⁺can also be adsorbed on the surface of Ca SO₄·2H₂O crystals to improve surface energy in a certain direction and promote crystal growth rate.In addition,the addition of Mg²⁺can enhance local supersaturation of the solution and the reaction process on the crystal surface,improving sulfate removal efficiency.The actual wastewater validation experiment shows that steel slag has a better sulfate efficiency in actual acidic mine wastewater,reaching 58.72%.