The Research On The Preparations And Properties Of Chromium-containing Spinel

Spinel with a cubic structure is found in the nature.Its chemical formula is AB₂O₄,in which metal ions with different valence and different radius occupy either tetrahedral sites?A-sites?or octahedral sites?B-sites?,thus forming a variety of spinel.The simplest is binary spinel such as magnesium aluminate spinel?MgAl₂O₄?,magnesia chrome spinel?MgCr₂O₄?,The complex spinel solid solution,such as(Mg,Fe²⁺)(Al,Cr,Fe³⁺)₂O₄ exists widely in natural chromite and stainless steel slag.The chromium content in nature chromite is high,the beneficiation and thereafter the refining technology are nature.However,the chromium content in stainless steel slag is low?2 10 wt% Cr2O3?and is hard to recycle.Moreover,even the chromium exists as Cr³⁺ in stainless steel slag,Cr³⁺ will be gradually transformed into Cr6+ under the action of CaO in the natural conditions.The water soluble and mobile Cr6+ can be released into the environment and bring harm to human health and the growth of plants and animals.In order to eliminate the environmental pollution problems of stainless steel slag and to make full use of chrome resources,this paper tried to extract the chromium element from stainless steel slag and to synthesize spinel based on the acidolysis.With an aim to better understand the structure and properties of chromium-containing spinel,Mg(Al,Cr,Fe³⁺)₂O₄ spinel without Fe²⁺ was prepared by sol-gel method to study the effect of Cr content on the structure and properties.(Mg,Fe²⁺)(Al,Cr,Fe³⁺)₂O₄ was synthesized by molten salt method in order to investigate the effect of chromium and Fe²⁺ on their structures and performances.By using X-ray diffraction?XRD?,scanning electron microscopy and energy dispersive spectroscopy?SEM-EDS?,infrared spectrum?FT-IR?,we explored the composition,structure and morphology of the as-received spinel powders.The physical property measurement system?PPMS?,M?ssbauer spectroscopy?MS?and electron paramagnetic resonance?EPR?were used to determine the magnetic properties of samples.The main research contents and results are as follows:?1?Chromium-containing spinel was prepared from stainless steel slag by acidolysis.The converter slag and electric furnace slag were used as the raw materials.When the concentrated sulfuric acid was used,we can remove a large number of Ca,Si from stainless steel slag by forming gypsum and silicic acid.The filtrate containing many valuable ions was freeze-dried and then roasted at 1300 ?.The results showed that converter slag by sulfuric acid acidolysis can form MgFe₂O₄ spinel phase,but detected no chromium phase;electric furnace slag by sulfuric acid acidolysis can obtain?Mg,Fe??Cr,Al?₂O₄ multiple spinel phase and?Fe2SiO4?,indicating that the Si in the slag has not yet completely removed out,so the process needs to be improved further.When electric furnace slag was experimented by hydrochloric acid acidolysis,?Mg,Fe??Cr,Al?₂O₄ spinel was also obtained with a small amount of amorphous SiO2.Magnetization of the spinel series by hydrochloric acid acidolysis is much higher than that by sulfuric acid acidolysis.?2?Mg(Al_0.4Cr_xFe_1.6-x)O₄?x = 0,0.4,0.8,1.2,1.6?spinel series were prepared by sol-gel method.The results show that samples calcined at 800 ? characterize the formation of cubic spinel structure and appear well-shaped octahedral crystals.As an increase of calcination temperature,crystal size and crystallinity are increased,particle agglomeration is gradually aggravated.Under a certain calcining temperature,the lattice parameter and crytalline size decreases as the increase of x?Cr content?.M?H?curves of the simples calcined at 900 ? show that only the sample of x = 0.0 is saturated at 300 K,x = 0.0 and x = 0.4 reach saturation at 10 K.Combined with M?T?and M?H?,we found that the magnetization decrease markedly with the incorporation of increased Cr³⁺ ions.Then the magnetic properties of spinel are changed from ferrimagnetic paramagnetic to paramagnetic.?3?(Mg_0.8Fe_0.2)(Al_0.4Cr_xFe_1.6-x)O₄?x = 0,0.4,0.8,1.2,1.6?spinel series were prepared by molten salt under N₂ atmosphere,in which ferrous oxalate was used as a raw material to introduce Fe²⁺ into the spinel structure,with an aim to study its influence on structure and magnetic properties of the spinel.The results indicate that the spinel structure are successfully formed by the molten salt method at 1050 ? and show the octahedral morphology,We also observe that the grain size and the lattice parameters decrease,particle's agglomerations aggravated as an increase of x?Cr content?,M?H?curves show that samples of x = 0.0,0.4 and 0.8 can reach saturation at 10 K and 300 K,but the samples of x = 1.2 and 1.6 do not show a tendency to saturate even at maximum measured field of 5 T both at 10 K and 300 K.Seen from M?H?and M?T?curves,magnetization of samples is decreased with increasing of the Cr content,resulting the transformation of ferrimagnetic into paramagnetic.The magnetization is enhanced when Fe²⁺ is introduced into the spinel structure,and then superparamagnetic behaviours are also investigated from the samples of x = 1.2 and 1.6 from M?T?curves,M?H?curves and M?ssbauer spectra.