Classification and characteristics of main hazardous wastes in aluminum electrolysis process

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Classification and characteristics of main hazardous wastes in aluminum electrolysis processThe hazardous wastes produced in the process of electrolytic alumin

Classification and characteristics of main hazardous wastes in aluminum electrolysis process

The hazardous wastes produced in the process of electrolytic aluminum production mainly include: carbon slag, aluminum ash, overhaul slag, overhaul slag is divided into waste cathode and waste tank lining.  According to the National Hazardous Waste Catalogue, the waste residue generated by the maintenance and disposal of electrolytic cells in the process of electrolytic aluminum, and the salt residue and scum generated in the process of electrolytic aluminum are classified as hazardous waste.

In the process of aluminum electrolysis, the anode carbon block mainly reacts to generate carbon dioxide and carbon monoxide, and a small part of the carbon block does not participate in the electrochemical reaction and directly falls off from the anode to form carbon slag.  Its main components are C, ɑ-Al203, fluoaluminite and cryolite, with fluorine content up to 32%.

In aluminum electrolytic casting, aluminum alloy production process line will produce a variety of by-products, it is a mixture of aluminum metal and other components of aluminum oxide, known as aluminum slag, also known as aluminum ash.  The main components are oxides, aluminum, silicon, iron, magnesium oxides and potassium, sodium, calcium, magnesium and other metal chloride.  It contains 15% ~ 25% aluminum and 50% ~ 80% alumina.

In the aluminium cathode for carbon, for long-term immersion in electrolysis aluminum liquid, salt, liquid aluminum and the effects of stress and deformation and fracture occurs, the crack in the residual a large amount of fluoride, which C content is about 50% ~ 70%, the fluorine content of about 9.86%, and contains a small amount of sodium, aluminum, calcium, iron and silicon dioxide.

When the electrolytic cell is overhauled after several years of use, a large amount of waste cell lining (sin-sic) will be cleaned out. Because of long-term electrolyte erosion, a small amount of fluorine and cyanide will be contained, which is dangerous waste.

How to reduce carbon slag in aluminum electrolysis

Aluminum oxidation has natural oxidation, electrochemical oxidation, chemical oxidation, alkaline oxidation, acid oxidation, anodic oxidation, meaning that aluminum and aluminum alloy oxidation treatment method.

1. Manage Raw material supply well

The main Raw materials for carbon production, such as petroleum coke, coal pitch and calcined coke, should be selectively purchased, and used in combination according to the test results and anti-oxidation properties of carbon blocks. Measures should be taken to stop the supply of suppliers with unstable product quality.  For the mixed residual electrode, the electrolyte on the surface should be cleaned to minimize the electrolyte into the anode.

2, improve the processing quality of the anode production process

To improve the quality of carbon anode products, it is essential to improve the production quality of anode system, that is, the calcination quality of petroleum coke, molding formula, paste mixing temperature and kneading quality, raw block forming quality, raw block high temperature roasting quality.  Standardize the operation procedures, strictly implement the technical standards, to ensure that the surface and internal physical and chemical indicators of the anode meet the needs of electrolytic production.

3. Strengthen the analysis and inspection of trace elements

Affecting the quality of carbon anode, lead to affect the carbon anode in the electrolytic cell use effect and quality of aluminum trace elements, such as V, Na, Ca, Fe, S we will strictly control, cause a cell carbon anode slag strong elements of V, Na and other activity, should pay attention to, and by mixing ingredients and quality index, different regions to the proportion.

4. Improve the shape of anode carbon block, and adopt the anti-scouring anode carbon block without edges and corners on the lower surface.

The transition Angle between the side and bottom of the carbon block is changed from 90 degree Angle shape to chamfer shape or arc shape.  Through the test, it can be observed that the new electrode changed one day ago, the conductivity is very poor, but the lower edge Angle changed from right Angle to arc shape, indicating that the arc shape is mainly caused by electrolyte scouring the anode carbon block, and all the Angle of the carbon block becomes carbon slag into the electrolyte.  The main advantage of the carbon block without bottom edge is that it has strong scouring resistance and can effectively reduce the amount of carbon slag in the tank.