| Rubidium is an important rare metal and a strategic emerging industry metal.Rubidium mineral resources are relatively rich in China,but their grade is commonly low and most of them are associated with other resources,which make the extraction of rubidium challenging.Rubidium is currently recovered from the solution generated from the extraction of cesium and lithium from pollucite and lepidolite.The extraction of rubidium from mica,feldspar,and kaoline using chlorination roasting method has been reported in recent years.However,the current research only considers the recovery of rubidium,resulting in a low level of comprehensive utilization of resources.In additon,the chlorination roasting process has the drawback of large output of hydrogen chloride waste gas and wastewater with high salinity.Therefore,the research and development of clean and efficient rubidium extraction technology is of great significance.Recently,a large rubidium mineral resource has been found in China.In order to explore the feasibility of clean and efficient utilization and potential value of this rubidium resource,a systematic study on the comprehensive utilization of the rubidium resource was carried out in this paper.The technological mineralogy of the rubidium ore was initially studied using XRD,ICP,SEM-EDS,EPMA,and TG-DSC analysis.The results show that the main minerals in the ore are quartz,potassium feldspar,and micas.The mineral composition conforms to the characteristics of granite.Rubidium mainly exists in biotite,muscovite,and potassium feldspar as isomorphic substitute for potassium.The mineral composition and the occurrence state of rubidium and potassium determine that the destruction and dissociation of mica and feldspar is the necessary prerequisite for the efficient extraction of rubidium and potassium.On the basis of the thermodynamic calculation of the decomposition of mica and potassium feldspar with acid,the exploratory experiment on acid leaching of rubidium ore was carried out.It was found that the acid effectively dissolved the micas,but the dissolving of feldspar was limited,which makes it difficult to obtain high leaching ratios for Rb and K by direct acid leaching.Based on the experimental basis of acid leaching and the thermodynamics of sulfate decomposition and alkaline leaching of potassium feldspar calculated by FactSage software,an acid-alkali method was proposed.Micas were converted to sulfates by sulfuric acid curing.The optimum conditions for sulfuric acid curing were determined to be a temperature of 300?,a sulfuric acid dosage of 55%,and a time of 20 min.The desulfurization of sulfates was achieved by reductive roasting to release SO2,and thus the regeneration of sulfuric acid can be achieved.The sulfur removal ratio of 84.8%could be achieved at 750?,coal dosage of 5%,and time of 10 min.During the alkaline leaching,feldspar was converted into faujasite and cancrinite,meanwhile the Rb and K were leached into the solution.The optimum conditions for alkaline leaching were determined to be a leaching temperature of 150?,a liquid-solid ratio(mL/g)of 15:1,a NaOH concentration of 250 g/L and a leaching time of 1h.The high metal leaching rates(Rb 95.2%,K 92.8%)can be achieved using acid-alkali method.The acid-alkali method has the disadvantage of the long process,thus on the basis of the thermodynamics of alkaline leaching of mica calculated by FactSage software,the other high temperature hydrothermal alkaline leaching process was proposed.The optimum conditions of direct hydrothermal alkaline leaching are as follows:leaching temperature 230?,NaOH concentration 200 g/L,ore particle size 0.15 mm,liquid-solid ratio 10:1,leaching time 1 h,and stirring speed 500 rpm.The high metal leaching rates(Rb 95.1%and K 94.5%)were also obtained by direct hydrothermal alkaline leaching.The mechanism of alkaline extraction of rubidium and potassium from rubidium ore is as follows:K+and Rb+in mica and feldspar crystals were first dissolved into solution under hydrothermal conditions;Al-0 bond of Al-O-Si group in silica skeleton of mica and potassium feldspar was broken and the[AlO2]-anion group was formed in alkaline solution;Si-O-Si group was subsequently hydrolyzed to form[H3SiO4]-anion group;[H3SiO4]-and[A102]-reacted in the lye to form silica alumina gel containing silicon oxygen tetrahedron and aluminum oxygen tetrahedron;the silicon aluminum gel skeleton was converted into ordered crystal structure and filled with cation(Na+and Ca2+)to form faujasite and cancrinite.Compared with acid-alkali process,the alkali process has low energy consumption and is more concise,thus it is the preferred process.The leaching kinetics of rubidium ore shows that the leaching process is mainly controlled by internal diffusion.The leaching rate can be increased by increasing the leaching temperature and alkali concentration and reducing the particle size of rubidium ore.The preparation of wollastonite from alkali leaching liquor and the extraction and separation of rubidium and potassium were studied.The optimum conditions for desilication were determined to be a reaction temperature of 95?,a reaction time of 1h and a CaO/SiO2 ratio of 1.2.The optimum temperature for preparing wollastonite by calcining desilication product(calcium silicate hydrate)was determined to be 1100?.The optimum conditions for extracting rubidium from desiliconization solution are 1 mol/L t-BAMBP concentration(diluent xylene),3:1 O/A ratio,1.5 min mixing time and three stages.The optimum conditions for scrubbing potassium are 3:1 O/A ratio and ten stages.The optimum conditions for stripping rubidium are 4:1 O/A ratio,1 mol/L HCl and two stages.After the extraction,scrubbing and stripping,a 97%Rb recovery yield was obtained.The optimum conditions for extracting potassium from rubidium raffinate are as follows:1 mol/L t-BAMBP,(O/A)3:1,and two stages.The optimum conditions for scrubbing sodium are 4:1 O/A ratio and four stages.The optimum conditions for potassium stripping are 1 mol/L H2SO4 and(O/A)3:1.After extraction,washing and stripping,the recovery ratio of potassium reached 77%.The solution after K extraction can be returned to the leaching process by adding sodium hydroxide.Rubidium ore leaching residue has the same adsorption mechanism as zeolite,and good adsorption capacity for Pb2+.The adsorption of Pb2+by rubidium ore leaching residue conforms to the quasi-second-order kinetics equation.Under the conditions of equilibrium pH 7.3 and leaching residue dosage of 2.5 g/L,the removal ratio of Pb2+in solution containing 40 mg/L of Pb2+reached 99.6%.The adsorption isotherm of Pb2+conforms to the Langmuir model.The maximum adsorption capacity of the residue was close to that of zeolites and far greater than that of common industrial solid wastes,such as fly ash.Polyacrylamide can significantly improve the settling of the adsorbed residue. |
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