Study On Preparation And Adsorption Of High Performance Magnesium Hydroxide

With the development of industrialization and urbanization,water pollution becomes more and more serious,among which heavy metal pollution is very serious.Magnesium hydroxide,as an inorganic weak alkaline compound,is known as a green and safe water treatment agent,which has strong adsorption capacity and can remove heavy metal ions in water.The agglomeration of magnesium hydroxide obtained by direct hydration of light-burned magnesium oxide occurs during the reaction process,resulting in larger particle size and smaller specific surface area,weakening its adsorption property.Therefore,surface modification,such as dispersant,ultrasonic dispersion and mechanical ball milling,is needed to reduce agglomeration,refine grains and increase specific surface area.In this paper,the surface of magnesium hydroxide was modified by adding dispersant,ultrasonic dispersion and mechanical ball milling to prepare high performance magnesium hydroxide.The magnesium hydroxide before and after modification was used to adsorb heavy metal Cu2+,so as to evaluate its adsorption performance.The main conclusions are as follows:(1)According to the single factor experimental method,the hydration rate of lightburned magnesia was investigated,and the basic reaction conditions were determined as follows:the reaction temperature was 70℃,the reaction time was 2 h,and the stirring revolution was 700 r/min.Through particle size detection and SEM analysis,it was determined that MgNO3 and PGE-6000 had the best modification effect.When the content of magnesium nitrate is 3%,the average particle size Dv(50)was the smallest,which was 48.1 μm,and the specific surface area was 400.6 m2/kg;when the amount of PEG-6000 was 5%,the average particle size Dv(50)was the smallest,which was 50μm,and the specific surface area was 367.5 m2/kg.Through particle size detection and SEM analysis,it was determined that the optimal time for ultrasonic modification was 30 min,the average particle size Dv(50)was the smallest,which was 24.8 μm,and the specific surface area was 787.4 m2/kg.(2)Preparation of light-burned magnesia from magnesite by mechanical milling,drying and calcination,the average particle size of light-burned magnesia is reduced from 44.7 μm to 2.33 μm,the activity is increased from 77.99%to 89.77%,at the same temperature,the hydration time is shortened to 1 h,and the hydration rate is increased to over 99%.The optimum ratio and process conditions of two kinds of compound modifiers at atmospheric pressure and high pressure were obtained by orthogonal experiment,type C1:reaction temperature 70℃,reaction time 1 h,modifier dosage 7%,modifier ratio 3:1;type C2:reaction temperature 90℃,reaction time 1 h,modifier dosage 3%,modifier ratio 2:1:1;type Gi:reaction temperature 130℃,reaction time 150 min,modifier dosage 6%,modifier ratio 1:2;type G2:reaction temperature 110℃,reaction time 150 min,the amount of modifier is 4%,the ratio of modifier is 2:1:1.(3)Mechanical ball milling can accelerate the hydration of light-burned magnesia,reduce the particle size of product and refine the grain;the particle size of magnesium hydroxide can be reduced by increasing the mass ratio of ball/material;when single dispersant is used,the modified effect of MgNO3 is the best,the grain size is reduced,and the grains are mainly crisscross distributed,forming a cell like structure;when the composite dispersant is used,the effect of modification is the best when the dosage is 3%and the ratio of magnesium nitrate,polyethylene glycol-6000 and sodium dodecylbenzene sulfonate is 1:2:3.(4)Magnesium hydroxide is used to absorb Cu2+,and the removal rate is 99%,the amount of magnesium hydroxide before modification is 2 g/L,but only 1 g/L after modification;the removal rate and adsorption capacity of magnesium hydroxide for Cu2+ increase with the increase of adsorption time;increasing the temperature can promote the adsorption rate of Cu2+ on magnesium hydroxide;according to the correlation coefficient R2(R2>0.98),the adsorption process of magnesium hydroxide on Cu2+ is more suitable for Langmuir isotherm model,and the maximum theoretical absorption before and after modification is 303 mg/g and 529 mg/g respectively.The adsorption process of magnesium hydroxide to Cu2+ belongs to spontaneous physical adsorption,and increase of adsorption temperature,and the ΔG decreases;the enthalpy change ΔH>0,it shows that the adsorption of Cu2+ by magnesium hydroxide is an endothermic process,and the increase of adsorption temperature is beneficial to the adsorption of Cu2+;the entropy change ΔS>0,which indicates that the disorder degree of the system increases with the adsorption process;through the fitting analysis of the dynamic model,it can be concluded that:the adsorption of Cu2+by magnesium hydroxide is more in line with the pseudo second-order kinetic model.