Interests in the hydrometallurgical processing of primary sulfide concentrates have revived because leaching in chloride media is rapid and is capable of recovering sulfur in elemental form, and also because rapid advances are being made in corrosion-resistant materials.
A process is proposed which consists of low-temperature chlorination and selective oxidation of chalcopyrite concentrates to produce copper chlorides, elemental sulfur and ferric oxide. The copper chlorides are leached with an aqueous chloride solution, which will be separated and purified, and then electrolyzed to recover copper and regenerate chlorine for recycle. The process is based on a flowsheet reported on a Cu-Ni sulfide flotation concentrate(Smith and Iwasaki, 1985). Fluidized-bed reactors were chosen because of good gas-solid contacting capability, the ease of temperature control, and the ease of adaptability to continuous operation. Temperature control is critical since the phase diagram of the CuCl-FeCl3 system has two eutectics at 50% and 86% FeCl3 with melting points at 304°C and 263°C, respectively, and the exothermic nature of the reaction often leads to sticking of the bed ( hereinafter referred to as ‘fritting’ in this article) and interferes with the flow of solid particles through the reactor. Since sulfide minerals can be readily chlorinated near 200 °C, the fritting may be prevented by low temperature chlorination. However, sulfur chloride is reported to form in the presence of excess chlorine at this low temperature.
Materials: A dried and caked chalcopyrite concentrate, analyzing 28.68% Cu.23.76% Fe and 30.22% S, was first ground to -104um (100 mesh) and agglomerated into micro-pellets by adding an optimum amount of moisture together with 2% by weight of molasses as a binder, stirring in a bowl mixer, and then drying in an oven held at 105°C overnight. The micropellets had a size consist between 295 (48 mesh) to 74um (200 mesh) amounting to nearly 80% with a peak at 208/147um (70/100 mesh) fraction. For the present investigation, the 208/147um (70/100 mesh) fraction was used in most of the tests.
Apparatus: A fluidized bed reader with 50mm in diameter and 235mm in length was fabricated using heat-resistant glass with 30-degree angle cone at bottom and a flange ground joint at top. A 10mm diameter zirconia ball was placed in the conical bottom in order to hold the materials in place and also to act as a gas distributor. A schematic diagram of the reactor is shown in Figure I. For batch tests, the same reactor but without feed and discharge tubes was fabricated so that the dead zones will not occur between the reactor wall and these tubes during fluidization. The reactor was heated either with an electrically-heated split vertical furnace, or with a 200W ribbon healer, both controlled by an on-off PID controller with an alumel-chromel thermocouple placed near the outside wall of the reactor.
Sulfur liberated during chlorination was captured in a condenser consisting of three glass tubes of 35mm in diameter and 450mm in length, filled with 10mm pieces of 6mm diameter glass lubes. This condenser was found to be satisfactory for capturing finely divided sulfur fumes, and adopted for the present investigation. Alter passing the condenser, the effluent gas was washed in a water shower box before releasing to the atmosphere.
Chlorination behaviors of chalcopyrite concentrate was investigated in batch and continuous fluid bed reactors and operating characteristics of the reactors were ascertained. In spite of the high Cu content of the sulfide concentrate, no particular difficulties were experienced in its chlorination. Temperature was found to be the most important parameter; the higher the temperature, the lower the %S in the chlorination product may be attained. Reaction temperature of 240-250°C was chosen to approach the eutectic points of CuCl-FeCl3 phase diagram (304°C, 263 °C). In a preliminary test, however, an indication was given that the fluidization may be carried out at as high as 270-275°C.
To chlorinate thoroughly at a given temperature, the Cl2 concentration in the effluent gas should be controlled at about 100ppm in order to cercumbent the operational difficulties by the formation and vaporization of S2Cl2 and Fe2Cl6. It was demonstrated that this excess Cl2 could be reduced to undetectable level by placing a second reactor with a fluidizing bed of sulfide micro-pellets on top of the chlorination reactor. The chlorinated products thus prepared were not hygroscopic and had no deliquescent properties. The product was kept in capped bottles and used in the selective oxidation phase of the overall process.