During periods when resources were scarce, archaeological studies of ancient waste dumps show less household waste (such as ash, broken tools, and pottery), implying that more waste was recycled in place of new material. Recycling has been a common practice for most of human history, with recorded advocates as far back as Plato in the fourth century BC. 9.5 Possible income loss and social costs.5.1.3 Waste plastic pyrolysis to fuel oil.3.2 Recyclate Quality Action Plan (Scotland).removal and reuse of mercury from thermometers and thermostats). Another form of recycling is the salvage of constituent materials from complex products, due to either their intrinsic value (such as lead from car batteries and gold from printed circuit boards), or their hazardous nature (e.g. With other materials, this is often difficult or too expensive (compared with producing the same product from raw materials or other sources), so 'recycling' of many products and materials involves their reuse in producing different materials (for example, paperboard).

Some types of materials, such as metal cans, can be remanufactured again and again, indefinitely, without losing its purity. In ideal implementations, recycling a material produces a fresh supply of the same material-for example, used office paper would be converted into new office paper, and used polystyrene foam into new polystyrene. Materials for recycling are either delivered to a household recycling center or picked up from curbside bins, then sorted, cleaned, and reprocessed into new materials for manufacturing new products. The composting and other reuse of biodegradable waste-such as food and garden waste-is also a form of recycling. Recyclable materials include many kinds of glass, paper, cardboard, metal, plastic, tires, textiles, batteries, and electronics. There are some ISO standards related to recycling, such as ISO 15270:2008 for plastics waste and ISO 14001:2015 for environmental management control of recycling practice. It promotes environmental sustainability by removing raw material input and redirecting waste output in the economic system. Recycling is a key component of modern waste reduction and is the third component of the ' Reduce, Reuse, and Recycle' waste hierarchy. It can also prevent the waste of potentially useful materials and reduce the consumption of fresh raw materials, reducing energy use, air pollution (from incineration) and water pollution (from landfilling). It is an alternative to 'conventional' waste disposal that can save material and help lower greenhouse gas emissions. The recyclability of a material depends on its ability to reacquire the properties it had in its original state. The recovery of energy from waste materials is often included in this concept. Recycling is the process of converting waste materials into new materials and objects.

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