At the 2024 SMM 19th Lead and Zinc Conference and Lead and Zinc Technology Innovation Forum - Zinc Recycling Industry Salon hosted by SMM, Ding Ruoyu, SMM consultant, introduced the topic of "Future Development Trend of Comprehensive Utilization of Zinc-containing Waste". He said that the renewable resources industry is conducive to the construction of a circular economy, to ensure the safety of the base metal supply chain, and consistent with the "double carbon" goal, the future will continue to be supported by policies at all levels from the central to the local level, the future of mainland zinc oxide enterprises to go overseas will usher in a good situation, and the environmental compliance of production will also be improved.
Drivers of zinc-containing waste utilization
Zinc resource scarcity and supply chain security are the core drivers of zinc-containing waste utilization
As of 2023, the global zinc reserves (economically recoverable reserves) are 220 million metal tons, mainly distributed in Australia, China, Russia, Peru and other countries. Based on the output of 12 million metal tons in 2023, the static recoverable life of global zinc resources is 18.3 years, which is a low-mineable variety among base metals. For comparison, aluminium and copper have a minable life of 80 and 40 years, respectively.
The mainland is widely distributed with lead-zinc ore, rich in resource reserves, and has the characteristics of many poor ores and few rich ores, many co-associated components and few single components, and complex mineral-forming components. With the rapid increase in the mining volume of zinc ore in China in the past 20 years, and there are phenomena such as rich mining and abandonment of poverty, indiscriminate mining and indiscriminate mining in the mining process, more than 50% of the rich ore resources have been utilized, and the problem of resource dilution is prominent.
With the increase in the risk of overseas resource supply chains, the challenge of zinc resource supply in mainland China has been exacerbated.
Policy support for the application of zinc-containing waste
The data shows that the production of 1 ton of different recycled metals reduces CO2 emissions.
In the context of "dual carbon", the non-ferrous industry, as one of the "eight major industries" with high energy consumption, is facing extremely difficult challenges in energy conservation and carbon reduction. In addition to upgrading the smelting process and adopting renewable energy, secondary resource recycling is also one of the efficient ways to break through the dilemma of high energy consumption and low output.
It is estimated that the use of metal secondary resources can save energy by 85%-95% and reduce production costs by 50%-70%. In terms of metal items, according to the estimates of the China Association of Circular Economy, compared with the use of natural ore resources, each ton of recycled copper produced can reduce carbon dioxide emissions by about 2.8 tons, each ton of recycled aluminum production can reduce carbon dioxide emissions by about 14.6 tons, each ton of recycled lead production can reduce carbon dioxide emissions by about 1.75 tons, and every ton of recycled zinc production can reduce carbon dioxide emissions by about 2.43 tons
In recent years, the mainland has continued to introduce relevant policies that are favorable to the recycled metal industry at the national level, and local governments have also considered the actual local situation to match supporting policies, and the metal recycling, recycling and other industries have ushered in greater development opportunities, and the zinc-containing waste and recycled zinc industries are also among them.
Sustainable supply chains and corporate social responsibility are also important drivers of the use of zinc-containing renewable resources
In addition to policy factors, the supply chain and the pursuit of corporate social responsibility by enterprises themselves are also the driving forces for enterprises to carry out sustainable transformation.
The requirements of state-owned enterprises, foreign enterprises and overseas downstream customers for product carbon footprint and the use of recycled materials are transmitted to upstream enterprises along the supply chain, driving the further use of zinc-containing waste.
Current status of zinc-containing waste utilization
Introduction to common zinc-containing wastes
Steel mill dust removal:
Dust removal ash in steel mills refers to the dust collected by dust removal equipment such as electrostatic precipitators, gravity dust collectors and bag dust collectors in the production process of each process from sintering to steel rolling;
According to the source of production, steel ash can be divided into sintering head ash, blast furnace bag ash and converter dust removal ash. The material composition of different types of steel ash is often different and needs to be treated differently;
The composition of steel ash is more complex, in addition to iron, it generally contains alkali metals and alkaline earth metals, chlorine, silicon, zinc, carbon and other components. Alkali metals and alkaline earth metals make steel ash highly corrosive, and the presence of zinc will cause the zinc load in the furnace to gradually increase, causing harm to production.
Steel ash is used as a raw material to produce zinc oxide: under high-temperature reduction conditions, the oxide of zinc is reduced and gasified into zinc vapor and discharged along with the flue gas, so that the zinc is separated from the solid phase. In the gasification phase, zinc vapor is easily oxidized to form zinc oxide particles, which are collected in the flue gas treatment system together with soot.
Copper smelting soot:
In the process of smelting, blowing and refining of pyrometallurgical copper, the flue gas formed by the volatilization, oxidation or gas flow of low-boiling point elements such as Pb, Zn, and As in the copper concentrate, as well as the soot obtained by the flue gas of the waste heat boiler through the dust collection system;
The main components of copper soot are copper oxide, zinc oxide and lead oxide, and according to the chemical composition with the different sources and copper smelting processes, it contains copper, zinc, lead, arsenic, antimony, cadmium, tin, indium and other metals, which have high recovery value. The soot is oxidized to sulfate in contact with gases such as oxygen and sulfur dioxide in the flue gas during the flue gas escape. Therefore, valuable metals in soot are mainly in the form of metal oxides and metal sulfates, which are conducive to metal recovery.
The comprehensive utilization process of copper soot can be divided into four categories: pyrometallurgical method, semi-wet process, full wet process and metallurgical combination, among which the wet process has developed rapidly in recent years. The process is to use acid, alkali, salt and other metals to leach Cu, Zn, As, In and other metals, and then use different methods to treat the leaching solution and leaching residue respectively.
In addition to the traditional raw material steel ash, in recent years, with the improvement of the technical level of the industry, more and more zinc-containing wastes have begun to be applied, such as lead-zinc smelting soot, steelmaking sludge, lead-copper smelting water slag, zinc concentrate tailings, smelting water treatment sludge, etc.
Due to the large number of metals in these scraps, they have shifted from refining a single metal to comprehensive utilization of scraps, and the iron, lead, copper, zinc and other metals in the scrap can be recycled.
The supply of steel ash, a traditional raw material, is tight
In recent years, due to the impact of the "de-capacity" of the steel industry and the weak demand of the downstream industries represented by real estate, the steel output of the mainland has remained stable and has not risen sharply. As there is no hope for a V-shaped rebound in the real estate sector, the supply of steel and even steel ash will remain stable in the future. However, the production capacity of the zinc oxide industry is expanding, resulting in a tight supply of traditional steel ash raw materials.
In this context, non-traditional metal-containing scrap and comprehensive metal recycling will be further promoted.
Zinc-containing waste industry chain
Multiple factors have driven the increase in production capacity of zinc oxide in recent years
Multiple factors such as the injection of investment funds, the downstream extension of steel mill business and the improvement of process technology have contributed to the increase in zinc oxide production capacity. Specifically,
In terms of investment capital injection: Due to the low prosperity of the real estate industry in recent years, some entrepreneurs and investors have set their sights on the renewable resources industry with policy support and good prospects. Zinc oxide
The industry ushered in an "investment fever".
In recent years, the original zinc oxide enterprises have also expanded production by building new production lines and updating larger rotary kilns, which has led to the overall improvement of the industry's production capacity.
Downstream extension of steel mill business: In March 2021, 10 departments including the National Development and Reform Commission jointly issued the "Guiding Opinions on the Comprehensive Utilization of Bulk Solid Waste in the 14th Five-Year Plan", requiring innovation
The new comprehensive utilization model of bulk solid waste will promote "solid waste without leaving the factory" in the iron and steel metallurgical industry and strengthen the full quantitative utilization.
Driven by the policy, many steel mills have begun to build their own rotary kilns to process steel ash and produce zinc oxide.
Improvement of process technology: With the improvement of waste disposal technology, the zinc-containing waste used for the production of zinc oxide has expanded from steel ash, copper soot and lead-zinc smelting ash in the past to steelmaking sludge, smelter water treatment sludge, hydrosmelting leaching sludge and other wastes that were completely discarded before.
The expansion of raw material sources has led to the increase in the production capacity of zinc oxide.
The national policy is favorable for the import of qualified zinc oxide products
Due to the insufficient supply of zinc-containing raw materials such as steel ash in China, coupled with the fierce competition in the domestic zinc oxide industry, some Chinese enterprises choose to invest overseas;
Since zinc-containing raw materials such as steel ash are solid waste and cannot be exported to the mainland, these offshore enterprises can only build zinc oxide plants overseas. Raw materials such as steel ash purchased overseas are produced into zinc oxide, which is sold locally or exported to China.
At present, mainland enterprises going overseas are mainly concentrated in Southeast Asia, Russia, Kazakhstan, Zambia and other places. The raw materials of the enterprises set up in Southeast Asia are mainly steel ash produced by local steel mills, while the enterprises in Russia and Kazakhstan will also use lead-zinc ore and zinc oxide ore in addition to steel ash.
Steel ash raw materials in parts of Europe, such as the Balkans, are cheaper, but due to the extremely stringent environmental requirements, there are high risks associated with investing in Europe.
Imported zinc oxide needs to meet the relevant standards strictly (1/2)
According to the Announcement on Matters Concerning the Comprehensive Ban on the Import of Solid Waste (Announcement No. 53 [2020]), starting from January 1, 2021, the mainland will prohibit the import of solid waste in any way, and prohibit the dumping, stacking and disposal of solid waste outside the mainland;
Since Zinc Oxide is a zinc oxide-rich mixture produced from steel ash and other wastes, the content of zinc oxide may vary depending on the raw material, so it may be recognized as solid waste and returned by customs at the time of import. Since 2021, there have been a number of similar cases;
The product name of secondary zinc oxide at the time of import is "zinc oxide enrichment" (tariff code: 3824999980, mixture with zinc oxide content of 50% or more by weight), and the product must meet the requirements in the "Zinc Oxide Enrichment for Smelting" (YS/T 1343-2019) to avoid being identified as zinc-containing waste.
Zinc oxide imported from overseas by China needs to meet the requirements in the "Zinc Oxide Enrichment for Smelting" (YS/T 1343-2019):
Process source: zinc oxide enrichment for zinc smelting produced by pyrometallurgical volatilization and enrichment of zinc-containing materials;
Moisture: The moisture (mass fraction) in zinc oxide should not be more than 10%;
Appearance quality: zinc oxide should be in powder form, the color should be uniform, and foreign inclusions should not be mixed;
The chemical composition needs to meet the requirements of the above table.
If the imported goods cannot meet the above standards, they will be recognized as solid waste in accordance with the General Principles for Solid Waste Identification Standards (GB 34330-2017) and the Procedures for Identification of Solid Waste Attributes of Imported Goods
It was returned and fined for violating the Law of the People's Republic of China on the Prevention and Control of Environmental Pollution by Solid Waste.
Prospect of comprehensive utilization of zinc-containing waste
The recycling industry will receive continuous policy support
The renewable resources industry is conducive to building a circular economy, ensuring the safety of the base metal supply chain, and is consistent with the "dual carbon" goal, and will continue to receive support from policies at all levels from the central to the local government in the future.
Diversified sources of raw materials
There is no hope for a V-shaped rebound in the real estate industry, and the supply of traditional raw material steel ash will continue to remain tight, and with the improvement of the technological level, the utilization rate of non-traditional zinc-containing waste such as steelmaking sludge and water treatment sludge will be further improved.
The industrial concentration is low
At present, the distribution of zinc oxide enterprises is relatively scattered, and the industry concentration is low. In addition, under the promotion of policies, steel mills have begun to get involved in the production of zinc oxide, and the competition pattern has been further complicated.
Enterprises go overseas to usher in opportunities
Due to the tight supply of domestic raw materials and intensified competition, superimposed by national policies on the support of imported zinc oxide, the future of mainland zinc oxide enterprises will usher in a favorable future.
Cleaner production
Processes that utilize zinc-containing wastes by either fire or wet processes carry the risk of environmental contamination (waste or wastewater). In the context of "environmental protection is no trivial matter", the environmental compliance of zinc oxide production will also be improved.