Available on line at Association of the Chemical Engineers of Serbia AChE www.ache.org.rs/CICEQ Chemical Industry & Chemical Engineering Quarterly 19 (1) 25−35 (2013) CI&CEQ ASIM KÜNKÜL1 INVESTIGATION OF THE USE OF AMMONIUM ABDULVAHAP GÜLEZGIN2 1 ACETATE AS AN ALTERNATIVE LIXIVIANT IN NİZAMETTİN DEMİRKIRAN THE LEACHING OF MALACHITE ORE 1Chemical Engineering Department, Faculty of Solutions containing ammonia allow for selective leaching of copper from a Engineering, Inonu University, copper ore. In this study, the leaching and kinetics of malachite ore were Malatya, Turkey examined using ammonium acetate solutions as an alternative lixiviant. The 2Kırşehir Prison and Detention effects of some experimental parameters on the leaching of malachite ore House, Kırşehir, Kırşehir, Turkey were investigated. A kinetic model to represent the effects of these parameters SCIENTIFIC PAPER on the leaching rate was developed. It was determined that the leaching rate increased with increasing solution concentration, temperature and stirring UDC 546.56:66:549.743.12 speed, and decreasing particle size and solid-to-liquid ratio. It was found that the leaching reaction followed the mixed kinetic control model. The activation DOI 10.2298/CICEQ120113039K energy of this leaching process was determined to be 59.6 kJ mol-1. Conse- quently, it was determined that ammonium acetate solutions could be used as an effective leaching agent for copper extraction from malachite ore. Keywords: copper, kinetic, leaching, malachite. Metals are frequently produced after being ex- lues in the metal source pass into the solution by tracted from an ore or its concentrates because most dissolving in the leaching step [1,2]. of them are found in nature as compounds, such as Copper is among the most prevalent and valu- complex mixtures of sulfides, oxides, carbonates, sili- able metals used in the industry. It is used mostly in cates. The extraction of metals from metal sources the electrical and electronics industries because of its like ores, concentrates, and secondary metal sources high conductivity [4-6]. In nature, copper is generally (various industrial wastes), is carried out by pyrome- found in the form of sulfide and oxide minerals, such tallurgical or hydrometallurgical methods [1,2]. as azurite, malachite, tenorite, chrysocolla, bornite, Hydrometallurgy is essentially concerned with brochantite, enargite, chalcopyrite, chalcocite, covel- methods whereby metals, metal salts, or other metal lite [5,7,8]. At the present time, the production of cop- compounds are produced by means of chemical re- per is generally performed using the low grade oxi- actions involving aqueous and organic solutions [2]. It dized copper ores and secondary sources containing covers a large variety of processes ranging from the copper due to depletion of high grade sulfide copper leaching of metal values in an aqueous solvent through ores [9]. The hydrometallurgical methods are usually the purification of the solutions to the recovery of the preferred for the recovery of copper from the low metals or their compounds by chemical or electroche- grade oxidized copper ores because of low cost, short mical precipitation [2,3]. Leaching is the term applied construction time, operational simplicity, good perfor- to the process of recovering a metal from the metal mance, and environmental advantages [10]. For this source by a solvent or lixiviant, and it is the first step aim, the strong acids, such as HCl, HNO3, and H2SO4, of any hydrometallurgical process. The metallic va- are mostly used as the leaching reagents. Sulfuric acid is the preferred lixiviant for the leaching of the oxidized copper ores, like azurite, malachite, tenorite, and chrysocolla [5,8]. However, the acid leaching can Correspondening author: N. Demirkıran; Chemical Engineering be sometimes uneconomical because basic ores may Department, Faculty of Engineering, Inonu University, Malatya, cause excessive acid consumption during the leach- 44280, Turkey. E-mail: [email protected] ing process due to the gangue minerals. Furthermore, Paper received: 13 January, 2012 some undesired impurities in ore matrix can be also Paper revised: 20 March, 2012 Paper accepted: 10 May, 2012 dissolved along with the desired metal, and they pass 25 A. KÜNKÜL, A. GÜLEZGIN, N. DEMIRKIRAN: INVESTIGATION OF THE USE… CI&CEQ 19 (1)25−35 (2013) into the solution. Therefore, more basic lixiviants than rix, such as iron and aluminum, precipitate in the form inorganic acids (or weakly acidic reagents) may be of hydroxides. As a result of this, a high purity solution more favorable in the leaching processes, allowing can be obtained at the end of leaching. In addition, impurities in the solution to be separated more effec- ammonium acetate provides ammonium ions, which tively [11]. So, the solutions containing ammonia have contributes the protons (hydronium ions) required for been used as lixiviant for the leaching of various ores, the dissolution of basic malachite ore. Ammonia and such as magnesite [12], colemanite [13,14], ulexite hydronium ions produced by reaction in Eq. (2) play [15,16], smithsonite [17], and hemimorphite [18]. an important role in the dissolution process. Basically, In acid leaching of oxidized copper ores, the im- hydronium ions are responsible for the dissolution of purities passing from ore to solution cause some basic ore. On the other hand, ammonia can form the problems in further processing of the leaching solu- stable complexes with copper (II) ions passing from tion, such as electrowinning of copper [19]. For these ore to solution. The formation of copper amine com- reasons, basic or weakly acidic lixiviants containing plexes can ensure an increase in the dissolution of ammonia have been also used for the leaching of the malachite ore. The copper in the malachite ore is in oxidized copper ores [5, 19-24]. the form of CuCO3⋅Cu(OH)2. Thus, when malachite In ammoniacal leaching systems, the dissolution ore is added into ammonium acetate solution, the re- of ore is carried out at mildly acidic or basic condi- actions occurring during the leaching process are pro- tions, and ammonia can be recovered by evaporation bably as follows: at the end of the process. Furthermore, some metals, CuCO .Cu(OH) + 2H O+ → Cu2+ + CO + which pass into the solution during dissolution pro- 3 2 3 2 cess, precipitate because of the higher pH of solu- + 3H2O + Cu(OH)2 (4) tions containing ammonia. Besides, ammonia forms + 2+ Cu(OH)2 + 2H3O → Cu + 4H2O (5) stable complexes with copper ions, and this leads to an increase in the leaching rate of ore. Thus, ammo- Copper ions pass into the solution in the form of nia allows for selective extraction of the copper from the water-soluble copper amine complexes with am- ore, leaving the undesired components in the residue monia, and thus, no precipitation of any copper com- [19,25,26]. As a result, a high purity solution for reco- pound occurs in the solution. The formation reactions very of copper can be obtained at the end of such a of the copper-amine complexes are written as follows: 2+ 2+ leaching process. Cu + 2NH3 Cu(NH3)2 (6) The aims of this study were to investigate the Cu(NH ) 2+ + 2NH Cu(NH ) 2+ (7) usability of ammonium acetate solution as lixiviant in 3 2 3 3 4 2+ the leaching of malachite ore and to determine the It is reported that the Cu(NH3)2 formed during effects of the experimental parameters, including am- leaching reaction is an intermediate species, and it 2+ monium acetate concentration, solid-to-liquid ratio, converts to the stable complex of Cu(NH3)4 [5,18]. particle size, stirring speed, and reaction temperature. Consequently, the overall leaching reaction can Ammonium acetate, chosen as the solvent in be written as follows: this study, is the salt of a weak acid (acetic acid) and 2+ CuCO3.Cu(OH)2 + 4NH4CH3COO → 2Cu + 4NH3 + a weak base (ammonia). According to the following - + 4CH3COO + CO2 + 3H2O (8) reaction, it ionizes in an aqueous medium: Because leaching is an essential unit operation → + - NH4CH3COO NH4 + CH3COO (1) in the hydrometallurgical treatment of ores, the kinetic Ammonium and acetate both undergo hydroly- analysis of leaching reactions is required for the effi- sis, as shown in the following equations: cient design of leaching reactor to be used in a hyd- + + rometallurgical plant. The reactions occurring in the NH4 + H2O NH3 + H3O (2) leaching process are heterogeneous. Because of those - - CH3COO + H2O CH3COOH + OH (3) reasons, leaching reactions do not often obey simple first- and second-order kinetics. The kinetic analysis Ammonia/ammonium and acetic acid/acetate of these kinds of reactions is generally performed buffered systems form in the aqueous medium. Thus, using the heterogeneous reaction models [28,29]. pH of solution remains almost constant during leach- Thus, the kinetic analysis of leaching process prac- ing process. Ammonium acetate is a neutral salt, and ticed in this study has been made using the shrinking pH of leaching solution is near neutral value at the core model. end of dissolution process due to the formed buffer system [27]. This case can be an advantage in the leaching because some impurities present in ore mat- 26 A. KÜNKÜL, A. GÜLEZGIN, N. DEMIRKIRAN: INVESTIGATION OF THE USE… CI&CEQ 19 (1)25−35 (2013) MATERIAL AND METHODS plexometrically using EDTA solution as titrant and murexide as indicator. The fraction of dissolved cop- An oxidized ore sample (malachite) used in this per (x) was calculated as follows: leaching process was collected from Palu region Ela- x= (amount of copper passing to the zığ, Turkey. The ore sample was crushed, ground, solution)/(amount of copper in the malachite ore) and then sieved using ASTM standard test sieves to obtain desired particle size fractions. The mineralogi- RESULTS AND DISCUSSION cal analysis of malachite ore sample was performed using a Rigaku RadB-DMAX II X-ray diffractometer.