Technology: Non-ferrous metallurgy | 'Strict disease' | High arsenic soot
Arsenic in high-arsenic soot has always been a difficult problem in the non-ferrous metal smelting process. On the one hand, the non-ferrous metal smelting industry is the main source of human arsenic emissions to the natural environment; on the other hand, the elemental arsenic in minerals is also difficult Effective recovery, and will have a serious negative impact on the smelting process. Therefore, how to effectively treat the arsenic contained in minerals, making it harmless and efficient, has always been a concern of non-ferrous metal smelting.
Source of high arsenic soot
The so-called high arsenic soot, as the name implies, is the smelting dust with high arsenic content. High arsenic soot mainly comes from two aspects:
(1) One aspect is the roasting and smelting process of metal minerals such as copper, lead, zinc, etc. Since arsenic is mostly associated with these metals in nature, arsenic cannot be completely inhibited during beneficiation, so there will be a certain amount Arsenic is accompanied by valuable metals entering the smelting process, thereby entering the soot;
(2) On the other hand, it is from the pyrotechnic treatment of arsenic-containing non-ferrous metal smelting slag or arsenic-containing leaching waste liquid. Based on the source of high arsenic soot, which generally contains a large amount of copper, nickel, lead, antimony, etc. 3. Metals, depending on the minerals they are smelting, sometimes contain precious rare metals such as indium and antimony.
Toxicity of arsenic compounds
High arsenic dust contains a large amount of arsenic compounds. This compound is a prototrophic poison. For example, the well-known arsenic is mainly composed of arsenic trioxide (As2O3). Oral administration of 0.1 g of arsenic can cause death and is very dangerous. Therefore, high arsenic dust is typical. Dangerous solid waste.
Different forms of arsenic have different toxicity, and the toxicity order is AsH3>As(III)>As(V)>MMA(methyl胂)>DMA(dimethylhydrazine)>AB, AC(arsenyl betaine, arsenic bile Alkali). Obviously, AsH3 is the most toxic in arsenic compounds. Among them, As(III) easily reacts with the thiol group of the enzyme protein in the body to form a stable chelate, which makes the enzyme inactive, so As(III) Strong toxicity, such as arsenic, arsenic trichloride, arsenic acid, etc. are highly toxic substances.
High arsenic soot contains not only a large amount of valuable elements, but also has high recovery value, and also has serious environmental hazards. Therefore, how to efficiently and harmlessly treat high arsenic soot is imminent. However, due to complex composition, arsenic content Higher, and with the increasingly strict environmental protection requirements, it is difficult to recycle high-arsenic soot. Therefore, few domestic enterprises are willing to recycle such dust. At present, high-arsenic soot is mainly handled by storage, and a few Enterprises only recycle a small amount of valuable metals (such as indium). This treatment method can not only effectively recover a large amount of valuable metals in high-arsenic soot, but also increase the difficulty of processing subsequent environmental waste and environmental protection pressure. .
Hazard of high arsenic soot storage
As mentioned above, most of the main treatment methods for high-arsenic soot in China still remain in the method of storage delay. However, when high-arsenic soot is stored in the yard, due to rain erosion, soaking, microbial action, etc. The accumulation of a large amount of arsenic-containing soot will cause serious environmental pollution. In the stacking area, workers and nearby residents often develop chronic arsenic poisoning. The incidence of cancer is significantly higher than other populations, and the average life expectancy is shorter than other populations.
The pollution of water environment by arsenic-containing soot is mainly caused by rainwater scouring, which causes the soluble arsenic salt to be leached, so that arsenic compounds, heavy metal ions and suspended solids are transported along with surface water and cause pollution. In most parts of China, especially East China The vast area of South China, from April to September every year, generally high temperature and rain, this full hydrothermal condition is easy to increase the leaching of waste, the risk of pollution spread.
In addition, these arsenic-containing compounds also infiltrate due to gravity, and some of them directly enter the groundwater layer to migrate and diffuse along the long distance of the water, causing groundwater in the arsenic-containing dust accumulation area, and the arsenic content in the well water is increased. The arsenic-containing compound enters the groundwater layer in part, and the other part enters the soil to migrate and transform. It causes pollution. When this part of arsenic is transferred into the farmland ecological environment, the crops will be reduced, and the arsenic content in the agricultural and livestock products will increase. And through the food chain to cause harm to the human body.
Storage of solid waste
According to reports and records in the literature, since 1961, there have been more than 20 incidents of arsenic pollution poisoning in China. For example, in 1961, Hunan Xinhua, due to the open storage of arsenic-containing waste ore, arsenic salt infiltrated into drinking water, resulting in 308 people. Poisoning, 6 people died; in another example, in 2008, the Yangzong sea body in Chengjiang County, Yunnan Province was seriously polluted by arsenic. The arsenic in water and fish was seriously exceeded, which directly threatened the drinking water safety of more than 20,000 people in the surrounding lake area, and made the local ecological environment and Industrial and agricultural production suffered heavy losses.
Harmless treatment of high arsenic soot
In order to change the status quo of high arsenic soot, it is necessary to develop a new method for comprehensive treatment of valuable metals by high-arsenic soot from the root cause, to achieve reduction of high arsenic soot, resource and recycling, and to alleviate non-ferrous metal smelting. The environmental pressure of enterprises. The research of new methods should be based on three points:
(1) Harmless treatment of arsenic. As analyzed above, the reason why high arsenic soot has such a large hazard is that the elemental arsenic and its compounds are highly toxic, so if these substances are not handled properly, they will be natural. And human health brings immeasurable harm. Therefore, the harmlessness of arsenic is the primary task of dealing with high arsenic soot;
(2) Recycling of arsenic. As203 is the most common arsenic compound, commonly known as arsenic, white arsenic, white peony, etc. In addition to the dramatic toxicity of disguised discoloration, As203 is also widely used in industry, agriculture, and medicine. It is the main raw material for the preparation of arsenic derivatives. It can be used as a beverage additive, insecticide, herbicide, and also used in the preparation of drugs (aspartic acid, rosaxan). It can also be used for the preservation of wood and fur, glass discoloration, etc. On the basis of harmlessness, the economic benefits of arsenic should also be explored to achieve the goal of high arsenic soot recycling;
(3) Comprehensive recovery of high arsenic soot. The high content of valuable metals such as copper, nickel, lead and antimony in high arsenic soot can achieve the purpose of separating and recovering valuable metals such as lead, antimony and indium in high arsenic soot. High arsenic soot can be regarded as an important secondary resource, which can reduce the cost of industrial solid waste treatment and improve production efficiency, and realize the comprehensive recovery of soot and efficient use of resources.
In summary, in the treatment of high arsenic soot, the most common research idea is to first remove arsenic from it, and detoxify or recycle the arsenic that has been separated, and then carry out the remaining soot. Comprehensive recovery. At present, the selective recovery process of valuable elements such as copper, nickel and bismuth in soot is relatively mature. Therefore, the key to high arsenic soot treatment is the removal of arsenic.
For the process of arsenic removal in high arsenic soot, the main methods are as shown below.
Major domestic research scholars
1, School of Metallurgy and Environment, Central South University Professor Guo Xueyi, Research Group
The main research results are as follows:
High arsenic soot sodium hydroxide-sodium sulfide alkaline leaching arsenic removal
New Process for Preparation of Sodium Pyroantimonate by High Arsenic Soot Alkali Leaching Residue
Preparation of sodium arsenate by oxidation crystallization of high arsenic soot alkaline leaching solution
Metal element leaching behavior of high arsenic soot during NaOH-Na_2S alkali leaching
Method for removing arsenic from arsenic-containing solution
2, School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology Professor Xu Zhifeng
The main research results are as follows:
Thermodynamics of arsenious acid vulcanization in alkaline aqueous solution
Research progress in treatment of arsenic-containing wastewater
High copper high arsenic soot pressure leaching process
Study on arsenic leaching of arsenic by black copper mud by sodium hydroxide
Professor Xu Zhifeng used a wealth of case studies to analyze the new technology of arsenic removal by arsenic in copper smelting
to sum up
The composition of high arsenic soot is complex and the phase composition is unstable. For the different components of soot, the appropriate method should be used for arsenic removal. The removal of arsenic is related to the subsequent comprehensive recovery of valuable metals in soot, which is also related to human survival. The environment and water resources are safe, so the non-ferrous metallurgy industry must meet strict requirements, abide by standards, and safely handle. Research and development of arsenic in new fields, and continuously optimize the comprehensive utilization of high-arsenic soot, to turn waste into treasure, High arsenic soot will not become a burden on the environment, nor will it waste resources to achieve sustainable development.