A raffinate describes any material remaining from a chemical or mechanical process after a desired chemical or material is removed. It may describe a liquid or solid, and may be further processed in additional steps or treated as a waste material. Even if a raffinate is not used to recover additional products, it may require further treatment to avoid creating any environmental issues when sent to a landfill or disposal site.
When crude oil from the ground is processed in a refinery, a mixture of carbon-based petroleum products is produced. Similar products can be created from reactions of natural gas, or methane, to form complex organic, or carbon-containing, molecules. Different processes can be used to extract desired compounds, including distillation by boiling the liquids, or solvent or water extraction from liquids or solids. After any of these processes are complete, a raffinate remains that is often further processed to remove additional materials.
A common raffinate stream in petroleum processing is known as the C4 stream. The term C4 refers to the four carbons in the various molecules being processed. A C4 molecule is described as being in the butane family, and can include butene, isobutane and isobutylene. All have four carbons in their molecules, and are valuable as raw materials for plastics and fuels.
When a C4 stream is processed, each step produces one desired chemical, and the remaining material must be processed further or discarded. Each raffinate becomes the feedstock, or raw material, for the next extraction or distillation step. The remaining or residual product may be tars or heavy petroleum products not suitable for further processing or commercial sale.
Mining uses a combination of different steps to remove the desired metals from the unprocessed ore, or metal-containing earth or rock. Grinding and separating the ore by mechanical shakers or separators can be used to separate some metals from the rock. The rock, now considered a raffinate, is often treated chemically to extract or remove additional metals. In some cases, liquids from the chemical reactions are also raffinates, because they are processed in multiple steps to remove as much valuable metal as possible.
Chemical processing of many materials can create residues or waste products requiring special handling to prevent environmental contamination. Gold and other metal ores contain small amounts of radioactive compounds that can be concentrated in the raffinate stream. These materials may need further processing to minimize the risk to both people and the environment. Petroleum processing creates heavy tar-like compounds that may cause cancer in humans, and may need to be incinerated or processed further before disposal. Some of the chemicals used to process raffinates are hazardous, and need to be removed before disposal.