The iron and steel industry is an important part of Taiwan’s industrial foundation. In addition to two integrated steel mills that import iron ore for steelmaking, there are 19 electric-arc furnace (EAF) steelmaking plants that recycle scrap iron and re-smelt it into raw steel. About 190,000 tons of EAF dust and about 1.42 million tons of slag are generated during EAF steelmaking. With the efforts of the EAF steelmakers and recycling organizations, a circular economy model for urban mining of steel materials has been created to handle the EAF dust and slag, achieving the goal of “complete recycling, zero waste of resources.”
Landfilling was common in Taiwan in the 90s and illegal dumping often occurred. Then Taiwan’s large-scale iron and steel enterprises formed Taiwan Steel Union Corporation which began researching and developing processing technologies for steel materials. To date, the corporation’s processing capacity has reached an equilibrium for processing within the iron and steel industry. It has now begun to process the accumulated 170,000 metric tons of EAF dust that had been dumped over the years. Regarding the public’s concern over the disposal of furnace slag, a breakthrough has also been made in its stabilization technologies, allowing the recycled products to meet the quality requirements of public constructions.
Currently, three main types of waste, namely EAF dust, oxidizing slag, and reducing slag, are generated during EAF steelmaking in Taiwan’s iron and steel industry. These types of waste can now be processed into precious resources. For every metric ton of steel billet produced, approximately 2% of EAF dust is generated. The dust contains mainly zinc, lead and cadmium. Through the high-temperature smelting technology of a rotary kiln, not only can valuable metal resources such as zinc and lead be extracted and recycled into products such as "crude zinc oxide," hazardous dioxin materials contained in the EAF dust are also removed during the high-temperature combustion process.
Currently, since the zinc content of the EAF dust processed by domestic enterprises reaches 56~62%, which is 5~6% higher than the zinc content of natural zinc ore, about 90% of the products are exported to zinc smelters or chemical plants in Japan, Thailand and Europe to be refined into 99.995% pure zinc ingots or zinc oxide powder and other refined products. The remaining 10% is sold to domestic chemical plants to be refined into >98% zinc-oxide powder that is used as a rubber additive for tires or shoes. As such, a 100% cyclical use rate of the recycled material has been reached, completing the life-cycle circulation of metallic zinc in Taiwan’s circular economy of iron scrap. And a business opportunity to accept waste and charge both the upstream and downstream for waste and zinc oxide products has been formed. With as much as 85% of revenue coming from zinc oxide products and only 15% from accepting waste (including EAF dust), a business model of “turning waste into gold” has been successfully created.
In addition to EAF dust, furnace slag is generated during steelmaking. With content similar to building materials, furnace slag has always been anticipated to become a recycled building material. However, if the calcium and magnesium contained in it are not completely reacted during the stabilization process, swelling problem will occur and become a limiting factor for slag recycling.
To solve the swelling problem of furnace slag, recycling organizations in the EAF steelmaking industry have built fully automatic production lines with ultra-high pressure steam autoclaves for the stabilization of reducing slag. The process can quickly cook and stabilize reducing slag over three to six hours and make it into recycled aggregates. The aggregates can then be mixed with construction materials that are specially made by plants of ready mixed concrete and made into controlled low strength material (CLSM) and non-structural concrete. Additionally, a dedicated laboratory for swelling control has been set up to ensure the quality throughout the entire process, putting slag input materials, the stability of stabilized aggregates and the quality of final concrete products in check. It is to ensure that the recycled materials meet national standards and that the whole-process flow tracking and reporting, from the production source to products, are strictly implemented, effectively turning waste into resources that can be safely used by the public.
Taiwan is short on resources. Through the integration of the upstream and downstream of EAF steelmaking and technology innovation, upstream iron scrap is re-smelted into steel raw material to be reused, and downstream EAF dust and slag are manufactured into zinc oxide products by Taiwan Steel Union through high-temperature smelting and into recycled building materials by Taiwan Steel Resources Corporation through ultra-high pressure steam stabilization. A complete industrial resource recycling chain has thus been formed, realizing the vision of urban mining. The EPA will continue to promote the recycling of different waste resources and enhance source reduction, waste diversion and processing technologies through revision of relevant regulations and strengthened management and assistance for the industry. It aims to turn waste formerly deemed worthless into resources, thereby avoiding resource exploitation and environmental damage. This way, a model of circular economy is built in which materials can be recycled and reused, facilitating Taiwan’s advancement towards the goal of “resource circulation with zero waste,” a key strategy to achieve net-zero carbon emissions by 2050.
Excerpt from Major Environmental Policies, August 2022
- Environmental Protection Administration, R.O.C.(Taiwan)