Adsorption Properties Of Modified Biochar Microspheres On Cd²⁺ In Water

Biochar has a good effect on the adsorption of heavy metals and other pollutants in wastewater.However,biochar has attracted people's attention.However,due to its difficulty in separating from waste liquid,biochar has been widely used.Studies have shown that the combination of biochar and magnetic media makes the biochar magnetized,which in turn contributes to the solid-liquid separation under the action of a magnetic field.This is one of the effective methods to solve the pollution control of heavy metal-polluted waste liquids and achieves better results.Application effectiveness.In this study,aquatic plants Eichhornia crassipes(also known as water hyacinth)widely distributed in China's Yangtze River,Yellow River Basin and various provinces in South China were used to produce biochar material by pyrolysis at 300?,500? and 700?.The process of Fe-modified granulation(marked as BCT).Through series of adsorption experiments such as isothermal adsorption and adsorption kinetics,the effect of different biochar materials on the adsorption of Cd2+in wastewater and its mechanism were systematically studied.The main conclusions are as follows:(1)With the increase of temperature,the pore structure of the water hyacinth charcoal surface increases continuously,the pore size becomes smaller,and the pore structure becomes more and more developed.The specific surface area of water hyacinth charcoal is generally increased after modification,and the specific surface area of the modified water hyacinth carbon microspheres prepared at 300°.and 500?.increases from 2.5 and 8.0 m2/g before unmodified.The specific surface area of the modified water hyacinth carbon microspheres prepared at 700? to 20,45 m2/g was reduced from 209 m2/g to 95 m2/g compared to the unmodified water hyacinth carbon microspheres.The modification made the pH of the water hyacinth charcoal significantly improved.Whether it was modified or unmodified,the pH of the water hyacinth carbon microspheres at 500? was the highest among the three pyrolysis temperatures.(2)Except for 3-BC and 7-BCT,the other four kinds of water hyacinth carbon microspheres reached the adsorption equilibrium at that point of 15h,after which the adsorption amount slightly increased or decreased.The equilibrium adsorption capacity of 6 kinds of water hyacinth carbon microspheres is between 20-30 mg/g.The adsorption equilibrium time of 7-BCT is greater than 15 h,and the adsorption capacity is the strongest.The equilibrium adsorption capacity is more than 30 mg/g,and the adsorption amount is then slightly increased or decreased.The adsorption kinetics of Cd2+is faster on BCT than on BC.Only the pseudo-first-order kinetic model provided the best fit for the experimental data of 3-BC and 3-BCT;in addition to 3-BC and 3-BCT,the curves of the other four types of water hyacinth carbon microspheres can be used in the same level.Or pseudo-second-order kinetic model for fitting.The equilibrium adsorption amount fitted with the pseudo-first-order kinetic equation reached the maximum at 7-BCT,which was 32.7 mg/g.The equilibrium adsorption capacity fitted by the pseudo-second-order kinetic equation is larger than the unmodified condition under the modified conditions.The largest 7-BCT was 47.4 mg/g.With the increase of pyrolysis temperature,the adsorption rate of water hyacinth carbon microspheres is increasing.(3)The adsorption isotherms of Cd2+on six biochar microspheres at 24? are in good agreement with the Langmuir equation and Freundlich equation.The adsorption characteristics of modified and unmodified water hyacinth carbon microspheres to Cd2+are more in line with the Langmuir isotherm equation.It can be presumed that most of Cd2+adsorbed on the surface of water hyacinth carbon microspheres is mainly monolayer adsorption.The maximum amount of Cd2+absorbed by 7-BCT was 45.8 mg/g.Compared with unmodified biochar microspheres,the adsorption capacity of modified biochar microspheres increased by 24.1%-89.3%at the same pyrolysis temperature.After bio-char modification,the maximum adsorption of Cd2+increased with the increase of pyrolysis temperature.(4)The factors affecting biochar adsorption of heavy metal Cd2+include ambient temperature,pyrolysis temperature,pH,and initial concentration of Cd2+.The adsorption capacity of water hyacinth carbon microspheres increased first and then decreased as the pyrolysis temperature increased(from 300? to 500? to a maximum of 700?).With the increase of pH value,the adsorption of Cd2+by water hyacinth carbon microspheres increased first and then gradually became stable.When the pH value is greater than 4.0,the maximum adsorption capacity of the modified water hyacinth carbon microspheres is greater than the unmodified water hyacinth carbon microspheres.When the pH value was 6.0,all the other five kinds of water hyacinth carbon microspheres except 7-BC reached the maximum adsorption capacity.The modified water hyacinth carbon microspheres had uneven surface and distributed a large number of fine particles,and these particles were flooded.Between its pores,the specific surface area of the adsorbent is increased.The ability of the modified water hyacinth carbon microspheres to adsorb Cd2+is significantly better than that of the unmodified water hyacinth carbon microspheres.The adsorptive capacity of water hyacinth carbon microspheres showed a trend of gradual increase with the increase of the initial concentration of Cd2+.