Solid Solid Separations

In order to get a good separation, the solids present must be liberated: that is, not physically or chemically attached, be suspended in a liquid medium and the flotation kinetics of the materials must be different. One or more stages of separation may be needed, depending on the kinetics and chemistry of the separation. To achieve sharper separation when difference in flotation rate of components is not high and/or material is not completely liberated, complicated flowsheets including multiple recycle lines and regrinding are used. Regrinding operations for middlings are used to avoid over-grinding of the bulk of material as it would cause reduction in flotation rate and selectivity for fine particles. For finely disseminated ores, entrainment is a substantial factor reducing sharpness of separation. Entrainment is a process of particle transfer to froth without their attachment on to bubble surfaces. This phenomenon can be explained by movement of small particles in the wake behind the rising bubble or within the static layer of liquid surrounding it. In machines with intensive mixing (impeller cells) the entrainment can also be caused by local upward slurry flows. These flows are not present in columns therefore reducing overall entrainment intensity and improving separation efficiency. A classical flotation flowsheet includes several cleaning stages generally linked by recycle of the cleaner tailings to previous stages. When more than one material is floatable and separation depends only on degrees of hydrophobicity (molybdenite-chalcopyrite), four to six stages may be required. If insufficient recovery is achieved in the primary vessel (rougher flotation), scavenger cells may be used. In general, all stages do have a common separation goal. For example, silica (impurity) is floated away from hematite in a four stage iron ore circuit in Figure 4. This circuit, or variations of it, is common when the valuable product is hydrophilic or an underflow product of the column. The example gives four stages of separation; however, in many cases fewer stages are required.

The circuit for a hydrophobic product is shown in Figure 5. The second cleaner stage of this circuit is generally not needed unless the separation is between

Figure 4 Hydrophilic product, solid-solid four-stage separation circuit. Example of iron ore.
Figure 5 Hydrophobic product, solid-solid four-stage separation circuit. Example of copper or plastics float.

hydrophobic materials with similar flotation rates. As an example, this configuration or variations of it can be used in phosphate, copper, zinc and plastics separations, or for soil remediation.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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