| The waste cobalt-molybdenum catalyst is greatly used in ammonia plant. With the vigorous development of synthetic ammonia industry with coal as raw material, the amount of the cobalt-molybdenum is also growing, resulting in generating more and more the waste cobalt molybdenum catalyst. Only in the coal chemical for synthetic ammonia the amount of the waste cobalt-molybdenum was 1.2kg/ton synthetic ammonia. The waste cobalt-molybdenum catalyst contains heavy metal cobalt, molybdenum and light metal aluminum. Cobalt belongs to the iron series element, the main existing form is two valent ion, because of its non degradability it can cause great harm to human and environment; Similarly, although the molybdenum resources are rich in China, But because of the over exploitation and low recovery rate, molybdenum resources is becoming less and less.In recent years, more and more attention was focused on molybdenum recovery from the waste cobalt molybdenum catalyst. The recovery of cobalt and molybdenum from waste catalyst, not only has the obvious economic benefits, but also has the significant social and environmental benefits.The extraction and back-extraction process was used in this paper for the Co and Mo recovery from waste cobalt-molybdenum catalyst, the total research was divided into four parts:(l)The pretreatment of raw material. Roasting waste cobalt-molybdenum catalyst in order to convert sulfide into oxide. The calcined products were characterized by XRD and XPS, the calcined product was MoO3 and CoO. When the calcination temperature was 600℃, the roasting time was 5h, the waste spent catalyst has a maximum extraction rate of 98.67%.(2) The selection of extraction agent. P507 was used to extract the MoO22+ and Co2+. The results showed that the optimum extraction conditions was:for MoO22+, extractant concentration 15%(v%), O/A 3:1(v/v), stirring time 30min, and stirring speed 500r/min, followed by extraction temperature was 24℃, the extraction efficiency of MoO22+ was 88.73%; For Co2+, extractant concentration 15%(v%), O/A 3:1(v/v), stirring time 30min, and stirring speed 500r/min, followed by extraction temperature was 24℃, the extraction efficiency of Co2+ was 86.78%. Both the extraction efficiency can not reach 90%.(3) Experimental study on Synergistic Extraction. (P204+Cyanex272) and (P507+Cyanex272) were respectively used in extracting MoO22+ and Co2+. The results showed that the optimum extraction conditions for MoO22+ was that aqueous phase pH was 0.88-0.96, synergistic extraction ratio(P204:Cyanex272) was 4:1, extractant concentration 15%(v%), O/A 3:1(v/v), stirring time 20min, and stirring speed 500r/min, followed by extraction temperature was 24℃; and the optimum extraction conditions for Co2+ was that aqueous phase pH was 5.92-6.00, synergistic extraction ratio(P507:Cyanex272) was 1:4:, extractant concentration 10%(v%), O/A 3:1(v/v), stirring time 10min, and stirring speed 1000r/min, followed by extraction temperature was 24℃. Under the optimum conditions, the extraction efficiency of MoO22+ was 96.78% and Co2+ was 95.43%. After analyzing the composition of synergistic extraction complexes, we can conclude that this synergistic extraction mechanism was acceleration mechanism; and after researchingthe co-extraction equilibrium constants we can conclude that this synergistic extraction process was an exothermic process.(4) The optimum anti-extraction conditions for molybdenum was that the ammonia concentration was 5mol/L, the quality of ammonium was 3g, O/A was 3:1(v/v), the anti-extraction temperature was 24℃;The optimum anti-extraction conditions for cobalt was that (O/A) was 1:3, the anti-extraction temperature was 84℃, For the recovery of cobalt oxalate, the optimum feeding methods in precipitation process was a liquid-liquid feeding way(adding oxalic acid solution into liquid CoSO4 solution), the reaction temperature was 50℃.(5) The form of the final product were analyzed by XPS, the final product of cobalt and molybdenum was ammonium molybdate and cobalt oxalate respectivly. |
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