Study On The Preparation Of Ammonium Dimolybdate From Molybdenum Concentrate Pressurized Oxidized Ammonia Leaching Solution

In this paper,the separation of molybdenum and sulfur and the preparation of ammonium dimolybdate were carried out in the mixed solution of ammonium sulfate and ammonium molybdate,which was produced by the patent technology of ammonia leaching under pressure oxidation of molybdenum concentrate developed by the project team.A new process of"ammonium molybdate precipitated by sulphuric acid precipitation-ammonium diammonium dimolybdate dissolved by ammonium solution"was proposed.Compared with the original extraction and separation process,the process has the advantages of shorter process and more complete separation of molybdenum and sulfur,which is of great significance to the transformation of the patent technology.The mixed solution of ammonium sulfate and ammonium molybdate was obtained by extracting rhenium and purifying ammonia leaching solution under pressure oxidation of molybdenum concentrate.The pH and temperature of acid precipitation were investigated by precipitation of ammonium molybdate with sulphuric acid.The effect of acid precipitation time on the precipitation rate of molybdate and the sulfur content of ammonium molybdate was studied.The optimum conditions of acid precipitation were obtained as follows:the pH value of acid precipitation terminal point was 2.5,the acid precipitation temperature was 35?,the acid precipitation time was 0.5 h,and the stirring speed was 220 rpm.Under the optimized conditions,the precipitation rate of molybdate is 93.14%and the sulfur content of ammonium molybdate is less than 0.05%.In order to reduce the sulfur content in ammonium molybdate as much as possible,the form of sulfur in ammonium molybdate precipitation was analyzed and the washing test was carried out.The results showed that the product of acid precipitation was a mixture of molybdic acid and molybdenum sulfate under the usual pH value of 1.5.The sulfur content in the acid precipitated product is about 5%,which can not be removed by washing.When the pH value of acid precipitation is 2.5,the product of acid precipitation is mainly a mixture of ammonium molybdate,and the content of sulfur in the product is relatively low,which is mainly an entrainment of sulfate,which can be removed by washing.The sulfur elution rate is 97.45%and the dissolution loss rate of molybdenum is lower than 10%in the process of washing.The optimum technological conditions for the preparation of ammonium dimolybdate by ammonia dissolution and evaporation crystallization are as follows:the acid precipitation product is dissolved in molybdenum ammonia molar ratio 2.0,The initial volume of ammonium molybdate solution was 440ml and Mo concentration is 292.8 g/L?specific gravity is 1.34g/ml?,the initial pH value is about7,and the evaporation temperature is 75?.When the stirring speed is 140 rpm and the specific gravity of the final solution is 1.40 g/ml,1.5 g seed is added to induce nucleation,the final pH of the solution is 6,and the solution is filtered by vacuum.When the cake was dried at 95?for 2 h,the crystallization rate of ammonium dimolybdate was 75.9%.The product contained 56.37%molybdenum,0.0001%sulfur,0.0047%impurity,and the product was agglomerated,and d_?0.5?was 126.3?m,which was superior to the requirement of MSA-0 grade ammonium dimolybdate in GBT/3460-2007.Mo was adsorbed by D314 anion exchange resin in pH 2 containing 6.5 g/L of molybdenum.The saturated adsorption capacity of molybdenum was 198.77mg/ml wet resin.When the contact time was 60 min,the penetration point was 0.13 g/L Mo.the adsorption capacity of molybdenum was 100.4 mg/ml,and the desorption peak solution was obtained when the desorption solution was 2 times the volume of the resin,and the desorption contact time was 1 h after desorption of negative molybdenum resin with 5N ammonia solution.When the desorption solution is 2.5times the resin volume,the desorption is complete and the solution can return to acid precipitation.