Preparation,Modification And Adsorption Properties Of Dyes And Heavy Metals Of Bamboo-Based Biochar

The discharge of organic dyes and heavy metals is an important cause of water pollution.Among the existing repair technologies,the adsorption of biochar has the advantages of simple operation and low cost.However,there are problems,such as small surface and poor adsorption selectivity.In view of the above problems,bamboo-based porous biochar with high specific surface area was prepared by ball-milling and KOH activation using bamboo straw powder as raw material,and the adsorption behavior of organic dyes methylene blue（MB）and heavy metals(Pb²⁺,Cu²⁺)on biochar was studied.The main research contents and conclusions were as follows.1.The preparation process of bamboo-based biochar（BBC）by ball-milling was optimized through single-factor experiment and orthogonal test using bamboo powder as raw material.The preparation conditions were ball-milling time of 3 h,pyrolysis temperature of 700°C and pyrolysis time of 2 h.Under these conditions,the adsorption capacity of MB onto BBC was 4.14 mg/g,which was 3.45 times higher than that of non-ball-milling biochar（BC）.After ball-milling,the porosity and content of C-O-H and aromatic functional groups of BBC were improved,which enhanced the adsorption performance of MB on BBC.2.There was a strong correlation between activation temperature and the pore structure of biochar.In this study,the adsorbent calcined at 900℃was the best.It had the largest specific surface area of 562 m²/g and a total porosity of 0.46 cm³/g.The optimal adsorption conditions of bamboo-based porous biochar（KBBC-900）on MB were adsorbent dose of 2 g/L,p H value of 11 and temperature of 25°C.Under these conditions,the removal rate of MB was as high as 99.5%and the adsorption capacity was 67.46 mg/g.The adsorption capacity was 70.63%of the first time after the material was recycled for three cycles.The adsorption behavior was a spontaneous single-point endothermic process and dominated by chemical adsorption including electrostatic interactions,cation-πelectron interaction and redox reaction.The aromatic structure and C-O-H played a significant role in the adsorption of MB on KBBC-900.3.Coexisting dyes had a great influence on the adsorption of MB.In the single MB system,the adsorbent reached a balance in 20 min,and the adsorption capacity was 48.16 mg/g.In the MB-MV system,the competitive inhibition of MV reduced the adsorption capacity of MB to 46.72 mg/g,and the adsorption equilibrium time was extended to 60 min.In the MB-MGo system,the existence of MGo greatly promoted the adsorption of MB.The adsorption capacity of MB was significantly increased to63.34 mg/g,and the equilibrium time was extended to 120 min.In the ternary system,the limitation of the adsorption sites led to a decrease in the equilibrium adsorption capacity of all dyes and a longer equilibrium time.In each system,the adsorption of MB on KBBC-900 was chemical adsorption by a single-point way.4.In single heavy metal system,the optimal conditions for KBBC-900 to adsorb Pb²⁺and Cu²⁺were adsorbent of dose 2 g/L,p H value of 5.5 and temperature of 25°C.Under these conditions,the adsorption capacity of Pb²⁺and Cu²⁺were 12.28 mg/g and5.18 mg/g,respectively.The adsorption capacity of Pb²⁺and Cu²⁺onto KBBC-900was 84.42%and 80.53%,respectively,of the first time after the material was recycled for two cycles.After adsorbing,the specific surface area and porosity of KBBC-900were significantly reduced.The adsorption process dominated by chemical reactions was characterized by a single-point adsorption behavior.The adsorption mechanism of Cu²⁺was mainly complexation reaction and redox reaction.The adsorption mechanism of Pb²⁺was mainly cationic-πelectron reaction and redox reaction.The stronger adsorption capacity of KBBC-900 for Pb²⁺was determined by adsorption mechanism,atomic weight,ion radius and electronegativity of heavy metals.5.In the binary system,the inhibitory effect of Cu²⁺made the adsorption capacity of Pb²⁺reduce significantly,while the adsorption capacity of Cu²⁺was slightly stronger than that in the unit system.The adsorption curves were affected by the change of system.The adsorption curve of Pb²⁺changed from H-type to L-type,and the adsorption capacity was significantly reduced.It was a mono-layer adsorption.The adsorption curve of Cu²⁺changed from L-1 type to L-2 type,and the adsorption capacity increased to 6.66 mg/g.It was a multi-layer heterogeneous adsorption.