Experimental Study On Treatment Of Ionic Rare Earth Mine Tail Water By Biochar And Plants

The ammonia nitrogen pollution has been severe in the ion-type rare earth mining area's aquatic environment because many extracting agents remained and migrated.The four feedstocks,rice husks,sawdust,peanut husks,and biogas residues,were pyrolysis to prepare biochar.The absorption experiment runs to investigate the influence of raw materials and pyrolysis temperature on the biochar properties and the adsorption behavior of biochar on ammonia nitrogen and nitrate nitrogen.The effect of biochar adsorption coupled with plant uptake to remove ammonia nitrogen and nitrate nitrogen was studied by hydroponic experiments,so that the following main conclusions:(1)Rice Husk,Peanut Husks,Sawdust and Biogas Residue were prepared for biochar at300?and 500?.At high pyrolysis temperature(500?),the loss of H and O in the raw materials was faster,H/C and O/C decreased,so the degree of the aromatic ring of biochar increased,and the surface organic oxygen-containing functional groups increased.With the increase of pyrolysis temperature,the inorganic minerals in the raw materials were retained in the ash.Moreover,The p H of biochar is positively correlated with ash content and the degree of biochar's aromatization.The p H of four kinds of biochar at 500?is all greater than 9.The specific surface area of biochar prepared by the four raw materials at 500?was higher than that at 300?,and the specific surface area of rice husk and peanut husk biochar was the largest,which was 109.05 m²/g and 114.14 m²/g,respectively.The specific surface area was positively correlated with the micropore structure of biochar.(2)The specific surface area and functional groups are the critical parameters of biochar adsorption performance.Biochar at 500?has a better adsorption effect on ammonia nitrogen than that at 300?,and RHBC500(rice husk)and PHBC500(peanut husks)have the largest adsorption capacity,which is 20.25mg/g and 22.52mg/g,respectively.The isothermal adsorption of ammonia nitrogen by RHBC and PHBC fit the Langmuir model.The adsorption kinetics of ammonia nitrogen by RHBC is in line with the quasi-second-order kinetics.The adsorption kinetics of ammonia nitrogen by PHBC is in line with the quasi-first-order kinetics.The adsorption effect of biochar on ammonia nitrogen increases as the p H of the solution increases.Coexisting ions Fe³⁺and Al³⁺in the solution can inhibit the adsorption of ammonia nitrogen by biochar.The effect of biochar adsorption nitrate-nitrogen prepared at 500?was better than that at 300?,and the maximum adsorption capacity of PHBC500(peanut husks)and BRBC500(biogas residue)for nitrate-nitrogen was 1.01 mg/g and 0.80 mg/g,respectively.The isothermal adsorption model of PHBC for nitrate-nitrogen conforms to Langmuir,and the isothermal adsorption model of BRBC for nitrate-nitrogen conforms to the Freundlich model.The adsorption kinetics of biochar for nitrate-nitrogen conforms to the quasi-second-order kinetics.The reduction of the p H value of the solution promoted the adsorption effect of biochar on nitrate nitrogen.The adsorption capacity of biochar to ammonia nitrogen is much higher than that of nitrate nitrogen,mainly because the surface functional group of biochar is better than that of negative charge.(3)The hydroponic plant's experiments were carried,and biochar was used as an adsorption substrate.The static experiment results showed that the combination of RHBC300,PHBC300(peanut husks),and PHBC500(peanut husks)and canna had the best removal effect on ammonia nitrogen removal rates of 80.66%,91.29%,and 89.27%,respectively.Further dynamic experiments showed that the removal effect of RHBC300 and PHBC300 biochar coupled with Canna was relatively stable,with removal rates of 81.01%and 76.28%.Compared with the adsorption experiment,the hydroponic experiments show that biochar at 300?as adsorption substrate coupling plants to remove ammonia nitrogen is better than 500?,which is due to biochar soluble organic matter and trace elements content is higher at the low thermal decomposition temperature.To provides a better environment,promote plant assimilation of ammonia nitrogen.The nitrate-nitrogen removal results by biochar coupled with plant showed that BRBC300 and BRBC500 combined with Cana had the best nitrate-nitrogen removal effect,and the removal rates were 95.19%and 96.75%,respectively.The dynamic experiment results showed that PHBC500 coupled with Canna and BRBC300 coupled with Chlorophyllin had the most stable degradation effect on nitrate nitrogen,with the removal rates of 84.22%and 80.26%,respectively.The removal rate of ammonia nitrogen and nitrate nitrogen from rare-earth tailwater by biochar coupled with Canna was stable at more than 75%.