A new process for the thermal refining of zinc: A case study of technology development at Mintek

During the late 1990s Anglo American PLC was evaluating the Gamsberg zinc deposit in the Northern Cape Province. As the primary South African metallurgical technology provider, Mintek became involved in the evaluation of a pyrometallurgical process for the recovery of zinc from the Gamsberg deposit. During the 1980s and 1990s Mintek was instrumental in developing DC arc furnace technology for the metallurgical industry. This includes the patented Enviroplas(R) process for the treatment of zinc bearing waste materials. As a consequence Mintek has developed extensive expertise in the pyrometallurgical processing of zinc bearing materials. However, Mintek's technologies stopped with the production of Prime Western Grade (PWG) zinc. Early on in the evaluation of the Gamsberg project, it became evident that the refining of PWG zinc would play an important part in the economic viability of the project. At the time the only pyrometallurgical technology available for the refining of PWG zinc to Special High Grade (SHG) zinc was the New Jersey process. This process represents 50-year-old technology and has not undergone significant refinement since the technology was developed. in order to provide a complete pyrometallurgical flow sheet for possible implementation at Gamsberg, Mintek assessed the New Jersey process with a view to either improving the technology or developing a new technology appropriate to the 21 century. In 1998 Mintek convened a consortium consisting of Mintek, the University of Cape Town, Eskom Enterprises, Bateman Metals and Anglo American PLC. The consortium successfully applied to the innovation Fund for funding to develop a new process for the pyrometallurgical refining of PWG zinc to SHG zinc. The main aims of the project were to develop a new technology for pyrometallurgical zinc refining that conformed to the following: Decrease the production cost of SHG zinc metal to stimulate the development of the Gamsberg deposit. Be compatible with the current Enviroplas(R) process, preferably as an add-on to that process. Should use electrical energy to benefit from local price tariffs. The project commenced at the beginning of 2000 and consisted of three phases: an initial technology search and assessment of the fundamental aspects of zinc distillation. the design of a pilot plant for zinc refining. the manufacture, commissioning and operation of the pilot plant. A new technology based on a DC arc boiler feeding a packed distillation column was developed and during 2003 the project culminated in the successful operation of a 200 kg/h pilot plant. Ultimately, all of the aims of the project were met and the main outcome is that an advanced process for the pyrometallurgical refining of zinc (the Zincref process) has been developed. The main innovation of the technology was the switch from an energy transfer limited process to a mass transfer limited process (for which a patent has been registered).