Document Type : Original Research Paper

Authors

Mineral Processing, Engineering, Tarbiat Modares University, Tehran, Iran

Abstract

In this work, the mechanism of zinc hydroxide and ammine complexation in caustic and ammonia leaching is investigated by molecular modelling using the density functional theory method. The speciation of zinc complexes is defined based on the thermodynamic data and Pourbiax diagrams. The mechanism of Zn+2 complexation by hydroxide and ammine ligands is simulated by molecular modeling. The structure of reactants in the form of individual clusters is modelled using the density function theory. In order to compare the hydroxide and ammine species structures, the geometry studies are carried out as well. The ammoniacal salt effectiveness to improve the dissolution and stability of the ammine species is studied. The ligand single molecule interaction with a smithsonite molecule is done for a better understanding. Molecular modeling show that the zinc hydroxide species are more stable based on the higher reaction free energies. The reaction free energies decrease by adding the OH- and NH3 ions to the complexes from -30.12 kcal/mol to -16.943 kcal/mol, and -22.590 kcal/mol to 66.516 kcal/mol, respectively. The Zn-OH bonds are shorter than Zn-NH3, and the ammine species show more regular structures in comparison with the hydroxide structures. The change of free energies in the presence of ammoniacal salts indicate that the sulfate ions can significantly improve the dissolution of zinc oxide in ammonia. The smithsonite interaction with ammonia and hydroxide reveal that hydroxide ions lead to a higher interaction energy than ammonia (-36.396 vs. -28.238), which is consistent with the higher stability of hydroxide species. The results obtained well-explain the experimental results obtained before, and can be effectively used to optimize the alkaline leaching of zinc oxide ore. 

Keywords

[1]. Ju, S., Motang, T., Shenghai, Y. and Yingnian, L. (2005). Dissolution kinetics of smithsonite ore in ammonium chloride solution. Hydrometallurgy. 80 (1-2): 67-74.
[2]. Ghasemi, S.M.S. and Azizi, A. (2018). Alkaline leaching of lead and zinc by sodium hydroxide: kinetics modeling. Journal of materials research and technology. 7 (2): 118-125.
[3]. Frenay, J. (1985). Leaching of oxidized zinc ores in various media. Hydrometallurgy. 15 (2): 243-253.
[4]. Abdel-Aal, E.A. (2000). Kinetics of sulfuric acid leaching of low-grade zinc silicate ore. Hydrometallurgy. 55 (3): 247-254.
[5]. Espiari, S., Rashchi, F. and Sadrnezhaad, S.K. (2006). Hydrometallurgical treatment of tailings with high zinc content. Hydrometallurgy. 82 (1-2): 54-62.
[6]. Hurşit, M., Laçin, O. and Saraç, H. (2009). Dissolution kinetics of smithsonite ore as an alternative zinc source with an organic leach reagent. Journal of the Taiwan Institute of Chemical Engineers. 40 (1): 6-12.
[7]. Larba, R., Boukerche, I., Alane, N., Habbache, N., Djerad, S. and Tifouti, L. (2013). Citric acid as an alternative lixiviant for zinc oxide dissolution. Hydrometallurgy, 134, 117-123.
[8]. Irannajad, M., Meshkini, M. and Azadmehr, A.R. (2013). Leaching of zinc from low grade oxide ore using organic acid. Physicochemical Problems of Mineral Processing. 49 (2): 547-555.
[9]. Chen, A., wei Zhao, Z., Jia, X., Long, S., Huo, G. and Chen, X. (2009). Alkaline leaching Zn and its concomitant metals from refractory hemimorphite zinc oxide ore. Hydrometallurgy. 97 (3-4): 228-232.
[10]. Moradkhani, D., Rasouli, M., Behnian, D., Arjmandfar, H. and Ashtari, P. (2012). Selective zinc alkaline leaching optimization and cadmium sponge recovery by electrowinning from cold filter cake (CFC) residue. Hydrometallurgy, 115, 84-92.
[11]. Kamran Haghighi, H., Moradkhani, D., Sardari, M.H. and Sedaghat, B. (2015). Production of zinc powder from Co-Zn plant residue using selective alkaline leaching followed by electrowinning. Physicochemical Problems of Mineral Processing, 51.
[12]. Lee, H.S. and Piron, D.L. (1995). Kinetics of alkaline leaching of pure zinc oxide. Chemical Engineering Communications. 138 (1): 127-143.
[13]. Ma, S.J., Yang, J.L., Wang, G.F., Mo, W. and Su, X.J. (2011). Alkaline leaching of low grade complex zinc oxide ore. In Advanced Materials Research (Vol. 158, pp. 12-17). Trans Tech Publications Ltd.
[14]. Habashi, F. (1993). A textbook of hydrometallurgy, metallurgie extractive Quebec. Enr. Que., Canada.
[15]. Ehsani, A., Ehsani, I. and Obut, A. (2021). Preparation of different zinc compounds from a smithsonite ore through ammonia leaching and subsequent heat treatment. Physicochemical Problems of Mineral Processing.
[16]. Soltani, F., Darabi, H., Aram, R. and Ghadiri, M. (2021). Leaching and solvent extraction purification of zinc from Mehdiabad complex oxide ore. Scientific Reports. 11 (1): 1-11.
[17]. Jiang, T., Meng, F.Y., Gao, W., Zeng, Y., Su, H.H., Li, Q. and Zhong, Q. (2021). Leaching behavior of zinc from crude zinc oxide dust in ammonia leaching. Journal of Central South University. 28 (9): 2711-2723.
[18]. Wang, R.X., Tang, M.T., Yang, S.H., Zhagn, W.H., Tang, C.B., He, J. and Yang, J.G. (2008). Leaching kinetics of low grade zinc oxide ore in NH3-NH4Cl-H2O system. Journal of Central South University of Technology. 15 (5): 679-683.
[19]. Yin, Z., Ding, Z., Hu, H., Liu, K. and Chen, Q. (2010). Dissolution of zinc silicate (hemimorphite) with ammonia–ammonium chloride solution. Hydrometallurgy. 103 (1-4): 215-220.
[20]. Ding, Z., Yin, Z., Hu, H. and Chen, Q. (2010). Dissolution kinetics of zinc silicate (hemimorphite) in ammoniacal solution. Hydrometallurgy. 104 (2): 201-206.
[21]. Rao, S., Yang, T., Zhang, D., Liu, W., Chen, L., Hao, Z. and Wen, J. (2015). Leaching of low grade zinc oxide ores in NH4Cl–NH3 solutions with nitrilotriacetic acid as complexing agents. Hydrometallurgy. 158: 101-106.
[22]. Sinclair, R.J. (2005). The extractive metallurgy of zinc. Victoria: Australasian Institute of Mining and Metallurgy.
[23]. Liu, Z., Liu, Z., Li, Q., Yang, T. and Zhang, X. (2012). Leaching of hemimorphite in NH3–(NH4) 2SO4–H2O system and its mechanism. Hydrometallurgy, 125, 137-143.
[24]. Yang, K., Li, S.W., Zhang, L.B., Peng, J.H., Ma, A.Y. and Wang, B.B. (2016). Effects of sodium citrate on the ammonium sulfate recycled leaching of low-grade zinc oxide ores. High Temperature Materials and Processes. 35 (3): 275-281.
[25]. Yang, S.H., Hao, L.I., Sun, Y.W., Chen, Y.M., Tang, C.B. and Jing, H.E. (2016). Leaching kinetics of zinc silicate in ammonium chloride solution. Transactions of Nonferrous Metals Society of China. 26 (6): 1688-1695.
[26]. Liu, Z., Liu, Z., Li, Q., Cao, Z. and Yang, T. (2012). Dissolution behavior of willemite in the (NH4) 2SO4–NH3–H2O system. Hydrometallurgy, 125, 50-54.
[27]. Delley, B. (2000). From molecules to solids with the DMol 3 approach. The Journal of chemical physics. 113 (18): 7756-7764.
[28]. Klamt, A. and Schüürmann, G.J.G.J. (1993). COSMO: a new approach to dielectric screening in solvents with explicit expressions for the screening energy and its gradient. Journal of the Chemical Society, Perkin Transactions 2. (5): 799-805.
[29]. Hancock, R.D. and Bartolotti, L.J. (2005). Density functional theory-based prediction of the formation constants of complexes of ammonia in aqueous solution: Indications of the role of relativistic effects in the solution chemistry of gold (I). Inorganic chemistry. 44 (20): 7175-7183.
[30]. Gutten, O. and Rulisek, L. (2013). Predicting the stability constants of metal-ion complexes from first principles. Inorganic Chemistry. 52 (18): 10347-10355.
[31]. Yin, X., Opara, A., Du, H. and Miller, J.D. (2011). Molecular dynamics simulations of metal–cyanide complexes: Fundamental considerations in gold hydrometallurgy. Hydrometallurgy. 106 (1-2): 64-70.