废催化剂中钼酸镍、钼酸钴以及钨酸镍的碱浸出热力学分析

Thermodynamic Analysis on Alkaline Decomposition of Nickel and Cobalt Molybdates and Nickel Tungstate

废催化剂常含有一定量的积碳和硫，因此在回收处理时多采用焙烧处理脱碳脱硫。在焙烧含W，Mo，Ni，Co的废催化剂过程中会产生一定量的复合氧化物，此外新型钼酸镍、钼酸钴、钨酸镍催化剂也在大量使用。这类钨、钼酸盐由于稳定性较高，采用已有工艺极难处理。针对此类复合氧化物的分解问题，绘制了25℃下Me—Mo（W）-H2O系和Me-Mo（W）-NH3-H2O系Me-Mo（W）-EDTA-H2O系的热力学平衡图，并对NiMoO4，CoMoO4，NiWO4的碱浸出和配合物浸出进行了热力学分析。研究结果表明：NaOH分解的难易顺序为NiWO4〉CoMoO4〉Ni—MoO4；氨可极大地降低NiMoO4，CoMoO4，NiWO4在水溶液中的稳定性，氨性溶液中Ni，Mo，Co，W的平衡浓度比水溶液中提高了1×10^2-1×10^4倍（pH约为8～11），其分解难易次序为NiWO4〉NiMoO4〉CoMoO4；EDTA同样可极大提高NiMoO4，CoMoO4，NiWO4在水溶液分解的Ni，Co，Mo平衡浓度，在EDTA总浓度为1mol·L^-1的条件下，NiMoO4，CoMoO4分解的最高M，Co平衡浓度为1mol·L^-1，而NiWO4最高Ni平衡浓度仅为1×10^-5.08mol·L^-1（[Y]T=1mol·L^-13种复合氧化物在EDTA水溶液中分解的难易顺序为NiWO4〉NiMoO4〉CoMoO4。碱分解、氨浸出以及EDTA配合物浸出均可选择性浸出NiMoO4，CoMoO4，而NiWO4则需要采用同时回收载体氧化铝的高压高碱分解法。

Spent catalysts contained a lot of coke and sulfur to be removed by roasting in the recovering process. During calcination of the spent catalysts containing Mo, W, Ni and Co, some complicated oxides were generated. In addition, lots of new NiMoO4, CoMoO4 and NiWO4 catalysts were employed. The molybdates and tungstates were refractory in nature and difficult to be treated. Aiming at dealing with the mixed oxides, theoretical analysis on decomposition of mixed oxides like NiMoO4, CoMoO4 and NiWO4 in spent catalysts by basic solution was studied. Several thermodynamic equilibrium diagrams of Me-Mo（W）-H2O, Me-Mo（W）-NH3 -H2O and Me-Mo （W）-EDTA-H2O systems at 25 ℃ were established. Based on that, alkali and complexation extraction processes were discussed. The de- composition order in NaOH solution was that NiWO4 〉 CoMoO4 〉 NiMoO4. Besides, in ammonium solution, the equilibrium concentration could be effectively improved （1 × 10^2 -1 × 10^4 times that of aqueous solution at pH 8 - 11 ） and decomposition order in ammonium salt solution was that NiWO4 〉 NiMoO4 〉 CoMoO4. Moreover, for NiMoO4 and CoMoO4, equilibrium concentrations of Ni and Co could be in- creased to about 1 mol-L-1 , while only 1 × 10^-5.08s mol·L^-1 of Ni for NiWO4 in EDTA solution （ [Y]T = 1 mol·L^-1 ）. The decomposition order was that NiWO4 〉 NiMoO4 〉 CoMoO4 in the presence of EDTA. Ni, Co and Mo could be selectively recovered from NiMoO4 and Co- MoO4 by alkali or ammonia leaching. However, NiWO4 might be processed by high concentration NaOH at high temperature and pressure, along with dissolution of plenty of A1203.