Preparation Of Nano-MnO₂-Biochar Composites And Its Performance And Mechanism For Removal Of Copper And Cadmium From Aqueous Solution

Human activities such as mineral mining and processing,fertilizer application,and wastewater irrigation,have increased the speed of heavy metals?for example cadmium,copper,etc?into the water and soil environment,which has exceeded the environmental bearing capacity and caused a series of ecological and environmental problems.Heavy metals pollution is characterized by extensive,hidden,persistent,easy to accumulate and difficult to degrade,which can have negative effects on the structure and function of the ecosystem,and can accumulate in animals and plants through the food chain,endangering the health of living creatures and human beings.Therefore,how to reduce heavy metals?copper and cadmium?in the aquatic environment has become a current research hotspot and difficulty.The adsorption is a relatively convenient and useful method to remove heavy metals from wastewater,and core is to select absorbent materials that have highly adsorption capacity.Manganese oxide/carbon-based composites have been widely concerned because of their advantages of excellent adsorption properties and easy separation and regeneration.This study was based on the deeply understanding about the mechanism of the biochar baseed functional materials adsorbed copper?Cu?and cadmium?Cd?.The fixed bed was explored to evaluate the removal efficiency,and influence factors of nano manganese oxide-biochar composites,and to further reveal the nature of Nano manganese oxide–biochar composites?NMBCs?to remove heavy metals from the waterbody.It provides theoretical basis for the regulation of Cu or Cd polluted water environment.Nano manganese oxide–biochar composites were successfully synthesized through the reduction of potassium permanganate by ethanol in a biochar suspension.Determination of the adsorption characteristics of NMBCs for Cu?II?and Cd?II?showed that NMBCs have a much larger adsorption capacity for Cu?II?than biochar or nano MnO₂,with a maximum adsorption capacity of 142 mg/g.and 152.1 mg/g.The Cu?II?or Cd?II?sorption process has been described using a pseudo-second-order model?R²>0.99?.The adsorption capacity of NMBCs for Cu?II?or Cd?II?was enhanced by increasing the pH from 3 to 6.This process was endothermic,spontaneous,and Cu?II?uptake does not change with ionic strength.The Cu?II?or Cd?II?absorption mechanism mainly involve the formation of surface complexes with MnO₂ and O-containing groups.NMBCs may serve as low-cost adsorbents that are more effective in various environmental applications,such as wastewater treatment or remediation of heavy metal-contaminated soils.A continuous dynamic adsorption experiment of heavy metal was carried out with NMBCs as fixed bed filler.When the inflow velocity was 20 m L/min,the initial concentration of water was 20 mg/L,and the column height was 10 cm,the removal efficiency of NMBCs was much higher than that of BC.The penetration time and depletion time of NMBCs can be prolonged by reducing the inlet velocity.Increasing the height of the fixed bed increases the time required for absorption to saturate.Thomas model can be used in the description of the dynamic adsorption process of Cu or Cd by NMBCs.The model fitting parameters can provide the effluent concentration and maximum adsorption parameters in the industrial application of NMBCs.The optimum conditions for the removal process of NMBCs are low concentration of solution,low flow rate and increased filler height.The effects of copper and cadmium concentration,different ions and acidity on the removal efficiency of fixed bed were studied by simulating electroplating plant wastewater.The results show that the fixed bed with NMBCs for Cu²⁺and Cd²⁺has better removal efficiency.In the given time,the greater the concentration of Cu²⁺and Cd²⁺in solution,the lower the efficiency of fixed bed,the removal rate was 50%and 60%,respectively.Divalent metal ions such as Ca²⁺and Mg²⁺could decrease efficiency of Cu²⁺and Cd²⁺by fixed bed significantly,which is higher than that of K⁺,and the influence of Mg²⁺larger than that of Ca²⁺.Increasing ion concentration,the removal efficiency of Cu²⁺and Cd²⁺by fixed bed is inhibited.The removal efficiency of Cu²⁺and Cd²⁺was increased with the increase of pH.At pH=6,the removal for heavy metal ions were the best.