A novel, low-energy process route for primary production of copper utilising synergistic hydro- and pyro-metallurgical processes

Abstract

In this thesis, a novel, low-energy process route for primary production of copper that utilises synergies between hydro-and pyro-metallurgical processes is proposed. The process involves precipitating copper from an acidic leach solution by pH adjustment. This precipitation step separates and concentrates the copper from the leach solution. The concentrated copper precipitate is then fed to a pyrometallurgical copper smelter or converter. Research on this process focused on four areas:• The copper phases produced by pH adjusted chemical precipitation from acidic solutions.• Factors affecting the kinetics of the copper precipitation step.• The thermal properties of the precipitated copper phases.• The mass and energy balance implications of feeding the precipitated copper product into a copper converter.The solubility of copper phases were determined by precipitating copper from solution and providing sufficient time for equilibrium to be established. In this study, the stabilities of precipitated copper oxide and basic copper sulphate, nitrate and chloride salts were determined over a pH range of 3 to 13 in solutions with ionic strength up to 3.5 M. The solubility products for the precipitated salts were calculated after taking into account the solution speciation, solution species activity coefficients and the surface energy associated with the fine particles. The standard Gibbs energy of formation of CuO tenorite, CuSO 4 .3Cu(OH) 2 brochantite, CuCl 2 .3Cu(OH) 2 clinoatacamite and Cu(NO ) 2 .3Cu(OH) 2 rouaite were estimated to be -124.9, -1,814.1, -1,341.6 and -1,278.5 kJ/mol respectively at 25°C.The copper precipitation kinetics and reaction mechanisms were then studied in the aqueous sulphate system, focusing on the use of limestone as the precipitation reagent. A range of precipitation conditions and reactor configurations were examined to determine which factors had significant effect on the rate of copper precipitation in this complex heterogeneous reaction system where limestone dissolution and co-crystallisation of brochantite and gypsum occur simultaneously. The rate of copper precipitation was initially limited by nucleation of the copper solid after which limestone dissolution was the limiting factor. The dissolution of limestone was dependent on the surface area of limestone, the concentration of copper and the hydrodynamic conditions within the reactor.

The Synergistic Copper Process concept

“…Experimental measurements have shown that moisture is progressively reduced on heating. Heating to 300°C will remove all water of crystallisation associated with the gypsum, while heating further to 450°C will decompose all of the hydroxides associated with the basic copper sulphate, expelling steam and leaving copper oxides and sulphates (Hawker 2015). The process flow diagram showing this variant is shown in Figure 4.…”

“…The liquidus temperature of the fayalite slags in copper converter slags is shown in Figure 9. Thermochemical calculations have also been undertaken to examine the potential use of PCP as a direct feed into copper converter technologies, and the effects of technology, matte grade, slag composition, and oxygen enrichment on the output from these processes (Hawker et al 2014;Hawker 2015). These preliminary calculations clearly demonstrate that, in the case of copper converting, if copper reverts and other inert materials currently used to control reactor temperature were partially replaced by PCP copper, the productivity through the converter section of the plant could be increased by between 5 and 35% depending on the technology and operating practice.…”

“…The most applicable to this discussion would be to precipitate the copper as a copper oxide-type solid. In practice, the precipitation of copper from sulphate solutions can be achieved by the cooling of saturated solutions, or by pH adjustment resulting in the formation of a basic copper sulphate solid, most likely brochantite (CuSO 4 .3Cu(OH) 2 ), or its hydrated form, posnjakite (CuSO 4 .3Cu(OH) 2 .H 2 O) (Hawker 2015). The precipitation of the copper as an oxide or hydroxide through changing the pH requires only relatively cheap precipitation reagents, such as limestone.…”

“…The process conditions required to produce the precipitated copper product from aqueous sulphate solutions at 25°C have recently been established and are summarised in Figure 6.

Figure 6 The process conditions required to produce the precipitated copper product from aqueous sulphate solutions at 25°C, a( ) = 1 (Hawker 2015).

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“…The process conditions required to produce the precipitated copper product from aqueous sulphate solutions at 25°C, a( ) = 1 (Hawker 2015). …”