Controlled Preparation And Heavy Metal Adsorption Properties Of Porous Magnesium Oxide/Magnesium Hydroxide

With the continuous development of economic society,the arbitrary discharge of untreated industrial wastewater had led to serious environmental pollution.In particular,heavy metal wastewater is of particular concern due to high toxicity,stability,non-degradation,bioaccumulation,and carcinogenicity.Therefore,the effective treatment of heavy metal is of great significance to the virtuous circle of the global environment.Due to their advantages of environmentally friendly and low cost,porous magnesium oxide/magnesium hydroxide adsorption materials present great potential in the treatment of heavy metal wastewater.However,the current controllable preparations of magnesium oxide/magnesium hydroxide with high activity and high adsorption capacity still pose great challenges.Based on this concept,porous magnesium oxide/magnesium hydroxide with high activity and high specific surface were controllable synthesized by precipitation-pretreatment calcination or simple and recyclable hydrothermal method,deriving from the idea of calcining water loss correlation and crystal plane assembly regulation.Furthermore,its physicochemical structure and control mechanism were characterized and analyzed,and their adsorption performance and mechanism of removal of heavy metal Pb（II）/Cd（II）were also investigated.The main points of this dissertation are as follows:（1）Synthesis and regulation of porous magnesium oxide.Magnesium hydroxide precursors with different crystalline were prepared by different pretreatment methods.The effects of pretreatment conditions,calcination temperature,and heating rate on the crystal form,pore structure and specific surface of magnesium oxide were investigated.The results showed that the pretreatment methods and calcination temperature have a greater impact on the pore structure of the product magnesium oxide.Under the conditions of reflux pretreatment and calcination at400℃,the maximum specific surface area of the obtained porous magnesium oxide is 284 m~2/g.（2）Adsorption properties and mechanism of porous magnesium oxide.The prepared porous magnesium oxide was used to remove Pb（II）and Cd（II）ions from wastewater,and the effects of adsorbent systems,p H,coexisting cations,adsorption time,and initial concentration on the removal efficiency were discussed.The results showed that porous Mg O with large specific surface area（284 m~2/g）had better adsorption capacity for Pb（II）and Cd（II）,and the maximum adsorption capacity are 7946 mg/g and 2483 mg/g,respectively.The value of p H has little effect on adsorption performance.When cations Ni（II）or Co（II）coexist with the target adsorption ion Cd（II）in the solution,there is kinetic competition between them,which reduces the adsorption efficiency to less than 10%.The adsorption process is a typical chemical adsorption,involving the solid-liquid interface reaction process of Mg O hydration and cation exchange.（3）Controllable synthesis of coral-like hierarchical porous magnesium hydroxide.Coral-like porous magnesium hydroxide（HPMH）with different specific surface areas and pore volumes were controllable synthesized by one-step hydrothermal method.The effects of different concentrations of citric acid（CA）directing agent on the nanostructure,specific surface area and pore volume of HPMH products were investigated,and its control mechanism was explored.The results show that the growth and assembly of magnesium hydroxide crystal face conditions can be controlled by CA under hydrothermal,which is adsorbed on the 001 crystal face.And,stable coral-like porous Mg（OH）₂can be obtained in one step.In this process,CA is not consumed and can be recycled.（4）Adsorption properties and mechanism of coral-like porous magnesium hydroxide.The prepared coral-like porous magnesium hydroxide was used to treat Pb（II）and Cd（II）ions from wastewater,and the effects of adsorbent systems,p H,coexisting cations,adsorption time,and initial concentration on the removal efficiency were discussed.The results showed that MH-CA20had the fastest adsorption efficiency under the same adsorption conditions,and the maximum adsorption capacity was 4545 mg/g and 3571 mg/g,respectively.The value of p H and coexisting cations has little effect on adsorption properties.It is concluded that the adsorption mechanism of MH-CA20 belongs to the solid-liquid interfacial reactions involving cation exchange,through the analysis of adsorption kinetics model.