Preparation Of MnS-phosphoric Acid Modified Corncob Biochar And Study On Its Adsorption Performance For Cu(?) In Wastewater

Copper is one of the essential trace elements for the human body and plants,but excessive copper in industrial wastewater can easily lead to plant growth retardation,leaves susceptible to chlorosis and even plant death,and damage human organs.The"Emission Standard of Pollutants for Copper,Nickel and Cobalt Industries"(GB25467-2010)stipulates that the maximum discharge concentration of copper and its compounds in industrial wastewater is 0.5 mg·L^-1.Adsorption is a popular heavy metal wastewater treatment technology,and biochar is low-cost,porous and porous as a adsorbent.However,the adsorption capacity of biochar is limited,thus,the modification methods such as activation and loading of functional particles can be used for biochar to improve the physical and chemical properties of the biochar surface and increase the adsorption capacity of the biochar on Cu(?)in water.In this study,phosphoric acid modified corncob biochar was mixed with manganese chloride,ammonia,and thiourea to prepare Mn S-f BC(manganese sulfide-phosphoric acid modified biochar)composite by one-pot solvothermal method,and the adsorption performance of Mn S-f BC for Cu(?)in water was studied.The main contents are as follows:1.The biochar derived from corncob flour was activated with phosphoric acid to improve the physical and chemical properties of its surface.Then the phosphoric acid-modified biochar was mixed with chemicals(manganese chloride and thiourea)of different theoretical mass ratios in ammonia to prepare Mn S-f BC with different loading ratios.The theoretical mass ratio of manganese sulfide to phosphoric acid modified biochar was optimized to m(Mn S):m(f BC)=1:1.2.By comparing the adsorption performance of biochar before and after modification,it was found that when T=35?,initial concentration=1000 mg/L,pH=5,dosage=1 g/L,time=12 h,the adsorption capacity of Mn S-f BC for Cu(?)reached97.1 mg/g,which was much higher than that of BC(18.0 mg/g)and f BC(25.0 mg/g).When the initial concentration was?50 mg/L,the adsorption efficiency of the composite was close to 100%,and the equilibrium concentration was less than 0.5 mg/L,which met the emission requirements of the"Copper,Nickel,Cobalt Industrial Pollutant Emission Standard"(GB25467-2010).3.When the pH was at a range of 3?6,after the adsorption for Cu(?),the removal efficiency by Mn S-f BC was stable at 60?70%;the composite hardly dissolved Mn ions in pure water,and Mn ions dissolved more in Cu(?)solution,which indicated that the adsorption for Cu(?)by the composite was accompanied by the dissolution of Mn ions;the pH after adsorption was all around 6,which proved that the surface of the composite was alkaline.At pH 3 the removal efficiency was the largest(69.4%)because the small amount of Mn ions dissolution increased the adsorption sites and the H⁺concentration at this time had a very limited inhibitory effect on adsorption,indicating that Mn S-f BC was suitable for weakly acidic wastewater containing Cu(?).4.The increase in dosage significantly increased the removal efficiency of Mn S-f BC for Cu(?),but the unit adsorption capacity decreased.When the dosage was 1 g/L,the composite had both good removal efficiency and adsorption capacity.The higher the initial concentration,the larger the unit adsorption capacity,but after the initial concentration was?200 mg/L,the Mn dissolution didn't increase significantly.A higher temperature could promote the adsorption progress of Mn S-f BC for Cu(?).The adsorption reached equilibrium after the reaction time was 12 h.5.When T=35?,pH=5,and dosage=1 g/L,the results of the Langmuir model fitting showed that the maximum adsorption capacity of Mn S-f BC was 95.18 mg/g,which was close to the adsorption capacity at the initial concentration of 1000 mg/L(97.14 mg/g).The Freundlich model was more suitable for describing the adsorption process of Cu(?),indicating that it was a multilayer adsorption process.Thermodynamic analysis showed that the adsorption reaction was spontaneous and endothermic at room temperature(15?35?).The pseudo-second-order kinetic model fitted better with the experimental data,indicating that the adsorption process was mainly chemical.6.Pb²⁺,Cd²⁺,and Ni²⁺in the solution had competitive adsorption behavior with Cu²⁺.Among them,Pb²⁺had the greatest inhibitory effect on Cu²⁺adsorption,and it also greatly increased the amount of Mn ions dissolved out,which was higher than other coexisting ions.And Cd²⁺and Ni²⁺slightly reduced the amount of Mn ions dissolved out;too much Mn ions in the solution would also inhibit the adsorption of Cu²⁺,because too much Mn²⁺made the adsorption equilibrium move in the opposite direction;Ca²⁺,K⁺,Cl^-could also inhibit the dissolution of Mn ions,and they had little negative effect on adsorption.Among them,the inhibition of adsorption by divalent Ca²⁺was slightly stronger than that of K⁺and Cl^-.7.SEM,BET,XPS,XRD techniques were used to characterize the biochar before and after modification&before and after adsorption,and it's showed that the activation of phosphoric acid made the surface of the biochar rough,which was conducive to the loading manganese sulfide;after the manganese sulfide was loaded,the flakes filled the pores of the modified biochar,decreasing the specific surface area to 19.77 m²/g,but it was still 3 times that of the unmodified biochar;the main load on the surface of manganese sulfide-phosphoric acid modified biochar was?-Mn S,in addition to Mn(OH)₂;Cu S and Cu₂(OH)₃(NO₃)appear on the surface of the composite after adsorption.The main adsorption mechanism of Mn S-f BC on Cu(?)were ion exchange and surface chemical precipitation including:(1)S^2-from Mn S on the surface of the composite combined with Cu²⁺to form extremely insoluble Cu S;(2)Mn(OH)₂ on the surface of the composite and the OH^-generated by the hydrolysis reaction of S^2-dissociated from Mn S had reactions with Cu²⁺and NO₃^-to form a precipitate of basic copper nitrate Cu₂(OH)₃(NO₃).