| Iron is the second most abundant metal element in the earth’s crust,which is widely distributed in aerosol,natural water,soil,plants and animals.At present,the geochemical behavior of iron oxides and its environmental effects have become the focus of attention of scholars at home and abroad.Among many iron oxides,hematite has the highest thermal stability and is a common natural adsorbent in soil,water,sediment and other surface environments.Most of the previous studies on the interaction between hematite and environmental contaminants(such as oxygen-containing ions)use irregular hematite particles.In fact,hematite has many exposed facets,corresponding to different atomic structures,and surface reactivity is different.Therefore,it is of great geochemical and environmental significance to study the interaction between hematite and environmental contaminants(oxygen-containing ions)from the perspective of exposing specific facets.Based on this,this paper uses hydrothermal method to synthesize hematite exposed to specific crystal faces,and selects chromate and phosphate as typical oxygen-containing ion representatives to investigate the adsorption characteristics and mechanism of the two on different exposed specific facets of hematite.On this basis,the influence of environmental factors on the adsorption of chromate and phosphate on different facets of hematite is further investigated.The main research results and conclusions are as follows:(1)Hematite with main exposed {001} and {012} crystal faces was synthesized.The structure and surface properties were characterized by XRD,Raman,XPS,SEM,TEM,BET and Zeta potentials.It was found that the hematite of the main exposed {001} crystal plane is nano-hexagonal(HNPs)and the hematite of the main exposed {012} crystal plane is nanocubic(HNCs);the specific surface area and isoelectric point of HNPs are slightly lower than HNCs.Because the HNPs and HNCs synthesized by hydrothermal method have regular morphology and special exposed crystal surface,the adsorption mechanism of oxygencontaining ions on two hematite ores was studied.(2)The adsorption characteristics of hematite {001} and {012} crystals to chromate and phosphate are clarified.In the chromate(Cr(VI))adsorption system,the adsorption of Cr(VI)on the HNPs surface is mainly monolayer adsorption,while the adsorption of Cr(VI)on the HNCs surface is mainly multi-layer adsorption,and the adsorption process is mainly chemisorption and exothermic.In the adsorption system of phosphate(in terms of P),the adsorption of P on HNPs and HNCs surface is mainly multi-layer adsorption,and both adsorption processes are controlled by physical and chemical adsorption and are spontaneous and endothermic processes.Through DFT calculation and infrared spectrum analysis,the adsorption configurations of chromate and phosphate on hematite {001} crystal surface are single dentate and double dentate and double dentate.(3)The effects of environmental factors such as pH,low molecular organic acid and inorganic ion on adsorption of chromate and phosphate radicals on hematite {001} and {012}crystal surfaces were investigated.Under different pH conditions(3～9),the adsorption of chromate and phosphate on HNPs and HNCs decreased with the increase of pH,which was related to the surface charge of hematite and the forms of chromate and phosphate.The inhibition of HNPs and HNCs on the adsorption of chromate and phosphate was enhanced with the increase of the concentration of HNPs and HNCs.Inorganic anions inhibited the adsorption of chromate and phosphate by HNPs and HNCs,while cations promoted the adsorption of chromate and phosphate by HNPs and HNCs.The above research results not only help to understand the geochemical behavior and environmental effects of iron oxides in the surface environment from the perspective of crystal plane,but also provide scientific basis for pollution control and ecological restoration of the surface environment(soil,water and sediment). |
PDF Full Text Request