Extraction of Cobalt and Nickel from a Pyrrhotite Rich Tailings Sample via Bioleaching

Abstract

One area in food processing that is receiving increasing attention is extraction. This separation process involves two phases. The solvent is the material added to form a phase different from that where the material to be separated originally was present. Separation is achieved when the compound to be separated dissolves in the solvent while the rest of the components remain where they were originally. The two phases may be solid and liquid, immiscible liquid phases, or solid and gas. Solid-liquid extraction is also called leaching. In supercritical fluid extraction, gas at supercritical conditions contacts a solid or a liquid solution containing the solute. Extraction has been practiced in the vegetable oil industry for a long time. Oil from soybean, corn, and rice bran cannot be separated by mechanical pressing, therefore, solvent extraction is used for their recovery. In the production of olive oil, the product from the first pressing operation is the extra virgin olive oil, the residue after first press may be re-pressed to obtain the virgin olive oil, and further recovery of oil from the cake is done by solvent extraction. Oil from peanuts is recovered by mechanical pressing and extraction of the pressed cake to completely remove the oil. One characteristic of solvent extracted oilseed meal is the high quality of the residual protein, suitable for further processing into food-grade powders. They may also be texturized for use as food protein extenders. Extraction of spice oils and natural flavor extracts has also been practiced in the flavor industry. Interest in functional food additives used to fortify formulated food products has led to the development of extraction systems to separate useful ingredients from food processing waste and medicinal plants. Extraction is also used in the beet sugar industry to separate sugar from sugar beets. Sugar from sugar cane is separated by multistage mechanical expression with water added between stages. This process may also be considered a form of extraction. Roller mills used for mechanical expression of sugar cane juice is capital intensive and when breakdowns occur, the down time is usually very lengthy. It is also an energy intensive process, therefore, modern cane sugar processing plants are installing diffusers, a water extraction process, instead of the multiple roller mills previously used. In other areas of the food industry, water extraction is used to remove caffeine from coffee beans, and water extraction is used to prepare coffee and tea solubles for freeze or spray drying. Supercritical fluid extraction has been found to be effective for decaffeinating coffee and tea and for preparing unique flavor extracts from fruit and leaves of plants.