Waste materials are called secondary resources in my country, and secondary raw materials abroad. The recycling of secondary raw materials can not only save material consumption and reduce costs, but in some countries that lack raw materials but have very developed industries, it is even regarded as a strategic policy for national economic development. For example, the secondary materials recovered and used by the GDR from all over the country have occupied an irreplaceable and important position in the supply of raw materials throughout the country. According to reports, more than 70% of the materials required for steelmaking come from scrap steel recovered from various places. More than half of the materials required by the paper industry are waste paper and waste textiles recovered from various places, more than 70% of all kinds of packaging are recycled and used, and more than 20% of the lubricating oil needed throughout the country is from recycled waste Obtained from oil by picking. Even the glue and gelatin it needs are refined from recycled bones. It can be seen that the secondary materials recovered by the GDR have become an important source of materials.

　　In our country, we also attach great importance to the recycling and utilization of waste materials called secondary resources. Take Shanghai as an example. At the time of the Sixth Five-Year Plan from 1981 to 1985, the Yishan Training Plant extracted tin from 2942 tons of various waste lead and ash residue after tin recovery. 227.8 tons, with an average recovery rate of 7%, 1005 kg of gold and 220 tons of silver are recovered from various metal scraps, which is not only worth 88.03 million yuan, but also eliminates environmental pollution.