Magnesium Based Biochar For Removal Of Phosphate And Fluoride From Water

In recent years,with the development of economy and the rapid growth of population,a large amount of industrial wastewater and domestic sewage is discharged into water bodies,causing a series of water pollution problems.Eutrophication of water bodies is the most common problem in water and the impact of fluoride pollution is very widespread.Phosphate is one of the main factors that limiting the eutrophication of water body,reducing the content of phosphate in sewage is a main way to governance eutrophication.At the same time,phosphate is also a kind of indispensable scarce resources in ecosystem.Therefore,it is important to achieve the removal,recycle and reuse of phosphate in sewage.As one of the essential trace elements of the human body,fluoride has a wide range of the application in our daily life.It is an essential component for human body to maintain the normal development of bones,playing an important role in promoting the process of formation of teeth,nerves and bones.The suitable amount of fluoride can enhance the ruggedness of the bones and have a certain function of prevention and cure of dental caries.But excessive intake of fluoride can damage human health,causing fluorine spot tooth and skeletal fluorosis.Fluoride is a common pollution ion in water.About 80% of fluoride in drinking water can be absorbed by human and part of fluoride in food can be absorbed by human.So,drinking water is the main way for human to absorb fluoride.Biochar is a kind of insoluble,stable,highly aromatic and carbon-rich porous solid matters produced by slow pyrolysis at the high temperature in the case of hypoxia.Because of its porous structure,large porosity,high specific surface area and rich in a large number of functional groups,biochar is a kind of materials which is very promising for the treatment of pollutants in water,that has been the focus of research in recent years.In this paper,the way to obtain biochar?BC?with loading MgO crystals was the evaporation crystallization and high temperature calcination in the case of limiting oxygen by using peanut shells and MgCl₂·6H₂O as raw materials.The magnesium based biochar?MgO-BC?was used as the adsorbent to study the adsorption of phosphate and fluoride elements in water and focus on the laws of common influencing factors and related mechanisms.The main contents were as follows:The experimental results show that the best phosphate adsorption onto MgO-BC happened in the p H range of 7⁹,and strong acidic or basic media was unfavorable to the phosphate adsorption.Phosphate adsorption process could reach equilibrium within 540 min,and the kinetics curve could be fitted well by both pseudo-first and pseudo-second models.The related coefficients were 97.3% and 99.0%.MgO-BC exhibited highly selective capacity toward phosphate in the presence of competing Cl-1,HCO3-1 and NO3-at 10 times higher the phosphate concentration.In addition,phosphate adsorption onto MgO-BC could be described satisfactorily by Langmuir model with a fitting coefficient higher than 99%,and the maximal adsorption capacity calculated by Langmuir equation was 138.07 mg·g^-1.The adsorption capacity of phosphate by MgO-BC was much higher than the unmodified BC and other biochar-based sorbents.Experiments showed that the mechanism of MgO-BC between phosphate was based on nonspecific Inner-sphere by the influence of competitive ions and Fourier transform infrared spectroscopy?FTIR?.Furthermore,the composite material after the adsorption of phosphate can also be used as fertilizer into the soil.It achieves the reuse of the discarded phosphate.All the results validated that MgO-BC had a wide application prospect for the phosphate cleanup from the actual wastewater.The experimental results show that the best fluoride adsorption onto MgO-BC happened in the p H range of 6⁸,and strong acidic or basic media was unfavorable to the fluoride adsorption.Fluoride adsorption process could reach equilibrium within 480 min,and the kinetics curve could be fitted well by both pseudo-first and pseudo-second models.The related coefficients were 97.3% and 94%.MgO-BC exhibited highly selective capacity toward fluoride in the presence of competing Cl-1 and NO3-at 50 times higher the fluoride concentration.In addition,fluoride adsorption onto MgO-BC could be described satisfactorily by Langmuir model with a fitting coefficient higher than 99%,and the maximal adsorption capacity calculated by Langmuir equation was 62.12 mg·g^-1 at 298 K.With the increase of temperature,the the adsorption capacity of fluoride by MgO-BC was gradually increased.The results showed that the mechanism of MgO-BC between fluoride was the Inner-sphere effect by the influence of competitive ions and Fourier transform infrared spectroscopy?FTIR?.In this paper,the adsorption characteristics of phosphate and fluoride by MgO-BC were studied systematically.The effects of pH value,contacting time and competitive ions on the adsorption of phosphate and fluoride were discussed.So as to provide the theoretical basis and technical support for the removal of phosphate and fluoride pollution in water.