| Layered Double Hydroxides(LDHs),a classic anionic laminar clay material,are composed of positively charged type of brucite structure layer board and negatively charged exchangeable interlayer anions.LDHs have good thermal stability,and have wide application value in the field of photochemical,electrochemical magnetics,biomedical and environmental.In recent years,LDHs has demonstrated a good application potential in the removal of organic and inorganic environmental pollutants as adsorption materials.In this paper,steelmaking slag is used as raw material,and the technological route includes selective leaching from steelmaking slag-controllable synthesis of LDHs-preparation of sound absorbing material by residue slag was proposed.The selective leaching of steel slag,preparation of sound absorbing material by residue slag and controllable synthesis of LDHs was studied.LDHs and its roasting products as adsorbents for the removal of pollutants in printing and dyeing wastewater and heavy metal wastewater were also carried out.The main contents and conclusions are as follows.(1)The influence of stirring speed,acid to slag ratio,initial acid concentration and reaction temperature and reaction time on the selective leaching of Ca/Mg/Al/Fe from steelmaking slag were studied.The optimum process condition of selective leaching of steel slag is obtained as stirring speed is 400 min-1,initial acid concentration is 5 mol/L,acid to slag ratio is 25:1,reaction temperature is 90℃,and reaction time is 3h.Leaching kinetic equations for different elements were established,all leaching process are in accordance with Avrami equation,and diffusion control is the speed control step.The above research provides basic data for the priority control and engineering design of slag leaching process.(2)The relationship between the alkalinity,aging time and temperature,and the growth of LDHs crystal were studied,and the Ca-Mg-Al-Fe LDHs products with uniform structure and uniform dispersion are obtained.The results of sample analysis of each reaction condition can be seen that the grain size of the synthesized product is larger along the a axis than along the c axis,that is,the growth rate of the(110)crystal surface is faster than that of(003)crystal surface.At the same time,with the increase of aging time and aging temperature,the lattice parameter a,c and the interval c0 of the synthesized samples show the change trend of the decrease in the first and then increases,which means the aging temperature and aging time are the main factors affecting the grain size and spacing of LDHs,and have great influence on product structure.(3)The synthetic Ca-Mg-Al-Fe LDHs are used to absorb the methyl orange in the solution.The adsorption capacity could reach 148.93 mg/g at absorbent dose of 0.5 g/L,initial concentration of methyl orange of 100 mg/L,adsorbent temperature of 30℃.The adsorption kinetic data of LDHs for methyl orange in different temperatures are in accordance with the pseudo-second-order rate equation,adsorption isotherm are in accordance with the Langmuir model,and the thermodynamic analysis shows that adsorption is an exothermic process.In combination with the solution properties before and after absorption and the structural changes of LDHs,it was confirmed that methyl orange was adsorbed on the LDHs with interlayer ion exchange adsorption and surface adsorption.The adsorption layer on the outer surface includes the outer layer and the inner complexation layer formed by the electrostatic interaction.The application life of LDHs as methyl orange adsorbent was investigated by means of the experimental study of analytic-regeneration-roasting-resorption.(4)A series of layered bimetallic oxide(CLDHs)products were synthesized with LDHs as raw materials.Using the analysis methods such as XRD,FT-IR,BET,the structure parameters of the products were discussed.When the roasting temperature is 450℃,the layer structure of the product collapse,and the mixed metal oxide was got,the specific surface area of which is 1.6 times than LDHs.The synthetic CLDHs are used to absorb the Cr(Ⅵ)in the solution,and the results showed that CLDHs showed good removal ability for Cr(Ⅵ)with low concentration.The adsorption kinetic data of CLDHs for Cr(Ⅵ)in different temperatures are in accordance with the pseudo-second-order rate equation,adsorption isotherm are in accordance with the Langmuir model,and the thermodynamic analysis shows that adsorption is an exothermic process.In combination with the solution properties before and after absorption and the structural changes of CLDHs,it was confirmed that Cr(Ⅵ)is adsorbed on CLDHs by physical adsorption and anionic interplanting.The application life of CLDHs as Cr(Ⅵ)adsorbent was investigated by means of the experimental study of recalcine-adsorption.(5)The selective leaching residue is used to prepare sound absorbing material.The effect of sample pressure and cement addition on product performance was discussed.Meanwhile,the leaching liquid filtrate was used as raw material for the preparation of aragonite calcium carbonate microspheres.The whole process concept design of elective leaching of steelmaking slag-synthesize of LDHs-carbonate production-preparation of sound absorbing material is also carried out. |
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