Keith Liddell is the inventor of the Kell Process having conceived the process initially as a treatment route for concentrate from the UG2 reef. Chromite contained in UG2 concentrates presents problems in smelting, and limits are placed on the amount of chromite that flotation concentrates can contain which reduces flotation recovery. Kell was designed to remove this constraint and it is completely insensitive to chromite. Over the years of development Kell has been fine tuned through testing and engineering studies to be robust and flexible so that its operating conditions can be tuned to the needs of each concentrate processed.

Energy Savings

Large savings in electricity and energy consumption can be made compared to smelting. This is because the silicate gangue minerals comprising most of the concentrate weight pass though Kell without reacting, whereas smelting concentrate requires them to be heated to over 1,400C and melted.

The process

Kell comprises of three main unit operations (pressure oxidation, thermolysis and chlorination) all of which are conventional and in common use in the industry. The simplified process flow is given below:

The Kell Process consists of several commercially proven unit operations. S, Ni, Co and Cu are first selectively removed by use of a pressure oxidation step during which the dissolution of PGM is minimized. The residue from pressure oxidation is subjected to a thermal treatment to ensure efficient PGM recovery by subsequent chlorination. All the core steps are very similar to well proven conventional unit operations in common use, as are the subsequent metal recovery steps to provide marketable end products. A key feature of Kell is that the sulphate (base metal leach) and chloride (precious metal leach) medias are kept entirely separate, enabling the process chemistry to be controlled and materials selection simplified.

Intellectual Property and ownership

The Kell process has granted patents in South Africa, USA and Canada in name of K.S. Liddell. The patents cover the whole process across the range of conditions that have been found to give the high metal recoveries. Testwork does not commence until end users have signed a confidentiality and non disclosure agreement. Liddell has licensed Lifezone Ltd (incorporated Mauritius) with the exclusive rights to exploit the patents and technology. Non-exclusive licenses are available to end users in return for technology fees and NSR royalty.