CLEAR process, Duval

One, the CLEAR process, was investigated by Duval Corporation near Tucson, Arizona (29). It involves leaching copper concentrated with a metal chloride solution, separation of the copper by electrolysis, and regeneration of the leach solution in a continuous process carried out in a closed system. Elemental sulfur is recovered. Not far from the Duval plant, Cypms Mines Corporation operated a process known as Cymet. Sulfide concentrates undergo a two-step chloride solution leaching and are crystallized to obtain cuprous chloride crystals. Elemental sulfur is removed during this stage of the process. 

A systematic study of krypton adsorption on exfoliated graphite was subsequently undertaken by Thorny and co-workers (Thorny and Duval, 1969 Thorny et al., 1972). Their stepwise isotherm, determined at 77.3 K, is shown in Figure 4.1. The layer-by-layer nature of the physisorption process is clearly evident - at least up to four molecular layers. This isotherm shape is remarkably similar to that of the krypton isotherm on graphitized carbon black reported by Amberg et al., (1955). 

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