Gravity separation

Abstract: Recovery of metal values from waste printed circuit boards using physical beneficiation techniques was studied. A novel flowsheet using a combination of wet and dry unit operations was developed to achieve the separation of metals from non-metallic constituents. The wet concentration circuit consisted of flowing film concentration in tabling, flotation of plastics and enhanced gravity separation in multi-gravity separator. The dry purification circuit consisted of electrodynamic and electrostatic separation. Substantial enrichment of the ground powder with good recovery of metals was achieved using the flowsheet. The starting PCB powder, ground to −0.5 mm size, had about 23% total metal. Complete liberation of metals from plastics was achieved below 100 μm size. Metal values were found to be more abundant in the coarser sizes. A concentrate grade of over 93% total metal at a recovery of over 54% or a grade of 66% total metal at 95% recovery could be achieved using this flowsheet. Recovery of small and flat metal pieces was problematic in conventional gravity separation. Using gravity separation as a pre-concentration operation followed by flotation and enhanced gravity separation, these problems could be solved to a great extent and good recoveries could be achieved. The circuit has great potential to recover metal values from waste printed circuit boards in an industrial scale.

Abstract: A comparative review of various types of the main gravity separation devices, both in the recent past and present is presented. The application of each device is discussed in turn, with details of the variables involved and the respective advantages and disadvantages of the separators, together with explanatory diagrams illustrating the processes.

Abstract: Flotation is a gravity separation process that originated from processing of minerals, and has nowadays found wide application, for instance, in industrial waste-water treatment. It is also useful in the concentration of a variety of dissolved chemical species often following a sorption process. The present review paper focuses on the removal of heavy metal ions from aqueous solution. The process mechanisms involved are either sorptive flotation where metal bonding agents, including biosorbents, are added and the subsequent complexes are separated downstream by flotation or other conventional flotation techniques, such as ion flotation are used. In the laboratory experiments described in this paper, zinc has been used as an example, but in addition copper, nickel, arsenic, etc. are considered. A new hybrid flotation–microfiltration cell is also introduced. Copyright © 2010 Society of Chemical Industry