Yun Chen 2005 - Research On The Recycling Of Valuable Metals In Spent Al2o3-based Catalyst

Minerals Engineering 19 (2006) 94–97

Technical note

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Research on the recycling of valuable metals in spent Al2O3-based catalyst Yun Chen *, Qiming Feng, Yanhai Shao, Guofan Zhang, Leming Ou, Yiping Lu Department of Mineral Engineering, Central South University, Changsha, Hunan 410083, PR China Received 5 May 2005; accepted 23 June 2005 Available online 10 August 2005

Abstract A new technology was developed to recover multiple valuable elements in the spent Al2O3-based catalyst by X-ray phase analysis and exploratory experiments. The experiment results showed: In the condition of roasting temperature of 750 °C and roasting time of 30 min, mol ratio of Na2O: Al2O3 1.2, the leaching rate of alumina, vanadium and molybdenum in the spent catalyst is 97.2%, 95.8% and 98.9%, respectively. Vanadium and molybdenum in sodium aluminate solution can be recovered by barium hydroxide and barium aluminate, the precipitation rate of vanadium and molybdenum is 94.8% and 92.6%. Al(OH)3 is prepared from sodium aluminate solution with carbonation decomposition process, and the purity of Al2O3 is 99.9% after calcinations, the recovery of alumina can reach 90.6% in the whole process. The Ni–Co concentrate was leached by sulfuric acid, a nickel recovery of 98.2% and over 98.5% cobalt recovery was obtained respectively under the experimental condition of 30% (w/w) H2SO4, 80 °C, reaction time 4 h, liquid:solid ratio (8:1) by weight, stirring rate of 800 rpm. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Recycling; Roasting; Leaching; Waste processing

1. Introduction Spent catalysts contribute a significant amount of the solid wastes generated in the petrochemical industry (Anon, 2000). These spent catalysts have been discarded for landfill in the past, but environmental pollution of air, soil and ocean contaminated by these waste catalysts has become a serious problem. Increasing environmental concerns and legislation regarding the disposal of hazardous residues are forcing companies and countries to process their own waste products and residues, Spent hydroprocessing catalysts have been classified as hazard-

*

Corresponding author. Tel.: +86 731 8830227; fax: +86 731 8830913. E-mail address: [email protected] (Y. Chen). 0892-6875/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2005.06.008

ous wastes by the Environmental Protection Agency in the USA (Rapaport, 2000). In short, the spent catalyst wastes have become an environmental problem, and at the same time, it has presented an opportunity for a new business to rejuvenate, recycle and convert the spent catalyst to an environmentally acceptable safe material for recycle. Several alternative methods such as disposal in landfills, reclamation of metals, regeneration/rejuvenation and reuse, and utilization as raw materials to produce other useful products are available to the refiners to deal with the spent catalyst problem (Chang, 1998; Trimm, 2001; Marafi and Stanislaus, 2003). During the past decade, considerable research was devoted to the comprehensive utilization of spent Al2O3-based catalyst. A survey of literature revealed that the technology for recycling spent Al2O3-based catalyst by roasting–extraction method (US Patent 5,431,892, 1995; US Patent 6,180,072, 2001; Yoo,

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1998; Al-Mansi and Abdel, 2002; Chmielewski et al., 1997). In the present research, the main process of recovering metals from spent catalyst are roasting and solvent extraction (Inoue et al., 1995; Edward, 1996; Luo et al., 2003). Most of the valuable elements in the catalyst had been recovered, but as the main body of the catalyst, carrier Al2O3 failed to have a good recovery, and this also leads to another new pollution. Therefore, the aim of this paper was to recover valuable metals in spent Al2O3-based catalyst.

2. Materials and methods 2.1. Materials Spent catalyst (Ni 4.77%, Co 0.35%, Mo 0.48%, V 0.55%, Al2O3 70.95%) was obtained from the atmospheric residue hydrodesulfurization unit of China National Petroleum Company, the particle size is between 0.06 and 0.1 mm. Fig. 1 is the X-ray diffraction result of spent catalyst. 2.2. Method Mixing the catalyst and alkali in a certain proportion and then put the mixture in a furnace, roasting it and then dissolve it in water, this leads to the formation of sodium aluminate solution, filter the solution. The Ni– Co concentrate after filtering is leached with the sulfuric acid; the impurity of V and Mo in sodium aluminate solution is recovered by barium hydroxide and barium aluminate, and then Al(OH)3 is prepared from sodium aluminate solution with carbonation decomposition process, high quality Al2O3 is prepared by calcinations

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of Al(OH)3 at high temperature. Fig. 2 is the recovering flowsheet of spent catalyst.

3. Results and discussion 3.1. Roasting Mixing spent catalyst with alkali and roasting it at high temperature, vanadium, molybdenum and nickel turn into the oxide at first, and then these metal oxides react with alkali. In this process, sodium hydroxide was chosen to react with spent catalyst at high temperature because the main form of alumina in catalyst is alpha-Al2O3 (Fig. 1). Under the condition of roasting at 750 °C for 30 min, mol ratio of Na2O: Al2O3 = 1.2, the leaching rate of alumina, vanadium and molybdenum in the spent catalyst is 97.2%, 95.8% and 98.9%, respectively, nickel and cobalt in Ni–Co concentrate are enriched (Ni 30.15%, Co 2.21%, Mo 0.07%, V 0.08%, Al2O3 10.37%). The dissolving of alumina disintegrates aluminates formed by aluminum and other valuable metals, and this is very significant for the next recovering of other valuable elements. 3.2. Recovering of V and Mo After roasting with alkali at high temperature, vanadium and molybdenum are dissolved in sodium aluminate solution in the dissolving process. In order to get high quality product of alumina, the impurity of V and Mo in sodium aluminate solution must be removed. Considering the low solubility of BaMoO4 and Ba3(VO4)2 in water (Xia and Fuenzalida, 2003; Oka et al., 1995). In this process, barium hydroxide and barium aluminate were added to recover V and Mo, respectively. With barium hydroxide, under the condition of 40 °C, reaction time 15 min, stoichiometric quantity of Ba(OH)2 (according to the chemical reaction), the precipitation rate of V is 94.8%; In the precipitation of molybdenum, 92.6% of Mo was precipitated under the condition of reaction time 40 min, 80 °C and the stoichiometric quantity of BaAl2O4 (according to the chemical reaction). Barium hydroxide and barium aluminate had no side effect on the decomposition of sodium aluminate solution. 3.3. Production of alumina

Fig. 1. The X-ray diffraction result of spent catalyst.

After the recovery of V and Mo by precipitation, the sodium aluminate solution was purified, the carbonation decomposition process was applied to the production of Al(OH)3, and then Al(OH)3 was calcinated at 1200 °C to produce alumina. The recovery of alumina can reach 90.6% in the whole process, and the purity of alumina

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Mixing (catalyst &alkali)

roasting

dissolving

Solid/liquid separation

Ba(OH)2

Acid leaching

Liquid

Solid/liquid separation

BaAl2O4

Ba3(VO4)2

liquid

Solid/liquid separation

CO2

Ni-Co concentrate

BaMoO4

Sodium aluminate solution

Al(OH)3

Al2O3 Fig. 2. Recovering flowsheet of spent catalyst.

is 99.9%, this quality is higher than the first class product of China
s national standard (Al2O3 is no less than 98.6%). 3.4. Acid leaching of Ni–Co concentrate The Ni–Co concentrate is a kind of metallurgical raw materials with high content of nickel and cobalt (Ni: 30.15%, Co: 2.21%). In each leaching experiment, 10 g Ni–Co concentrate was added to a certain amount of sulfuric acid having a specified concentration. Temperature, reaction time, liquid:solid ratio (L/S), stirring rate were adjusted. The reaction took place in a sealed container and the resulting slurry was filtered on sintered glass. The content of nickel and cobalt was determined by Atomic Absorption Spectroscopy. According to the results of exploratory experiments, the suitable leaching condition was 30% (w/w) H2SO4, L/S = 8, reaction time 4 h, 800 rpm, under this operating condition the leaching rate of nickel and cobalt can reach 98.2% and 98.5%, respectively.

4. Conclusions The catalyst wastes have rapidly been increasing worldwide. Recovering of valuable elements of spent catalyst became an unavoidable task not only for lowering the catalyst cost but also for reducing the catalyst waste to prevent the environmental pollution. Based on results obtained from the current work, the following conclusions are made: (1) By this novel process, the purity of alumina is 99.9% produced with carbonation decomposition process, the recovery of alumina can reach 90.6% in the whole process. (2) Under the suitable condition, with barium hydroxide and barium aluminate, the precipitation rate of vanadium and molybdenum is 94.8% and 92.6%, the precipitate can be sold as chemical product or further deep-processed. (3) The Ni–Co concentrate was leached by sulfuric acid, a nickel recovery of 98.2% and over 98.5%

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cobalt recovery was obtained respectively under the experimental condition of 30% (w/w) H2SO4, 80 °C, L/S = 8, reaction time 4 h, stirring rate of 800 rpm.

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