Pure aluminum phosphide is white crystal and is widely used due to its high insecticidal efficiency, economy and convenience. Aluminum phosphide can be used for granary fumigation. The aluminum phosphide content is 56.0% to 58.5%. Fumigation requires only 3 to 7 pieces per ton of grain, and only 1 to 2 pieces per cubic meter. The main toxicity of aluminum phosphide is that it decomposes rapidly when exposed to water or acid, releasing phosphine gas that is rapidly absorbed and highly toxic. A mixture with ammonium carbamate acts as a pesticide and is also used in welding. So how to deal with its residue?
Reason for residue treatment
The use of aluminum phosphide is accompanied by the generation of waste water, waste gas, and waste residue. Improper treatment of the three wastes will cause safety accidents and harm the environment.
1. Exhaust gas: Phosphine is a central nervous system depressant, irritating the respiratory tract, causing mucosal congestion, edema, alveolar congestion, and exudation. In severe cases, punctate and widespread bleeding, the alveoli are filled with bloody exudate, and phosphine passes through the alveoli. Absorbed throughout the body, affecting the central nervous system, heart, liver, kidneys and other organs.
2. Wastewater: Wet phosphine absorbs phosphine tail gas and produces phosphorus-containing wastewater, which can easily cause eutrophication of water bodies.
3. Waste residue: After 10 days of natural deliquescence of aluminum phosphide, the residue still contains no less than 2% of unreacted aluminum phosphide. When it comes into contact with water, it will generate phosphine, a highly toxic gas, which is prone to fire accidents.
Current status of aluminum phosphide residue treatment
1. Exhaust gas treatment methods: At present, warehouses mostly use natural ventilation for emissions. This method pollutes the surrounding environment and harms nearby activities. Phosphine purification treatment methods are divided into adsorption methods and chemical reaction methods.
The adsorption method uses adsorption materials to absorb phosphine in aluminum phosphide fumigation exhaust gas and remove phosphine in the exhaust gas, such as activated carbon adsorption.
Chemical reaction methods are divided into two categories: wet method and dry method. The wet method mainly uses the reducibility of phosphine to treat phosphine with an oxidant in the absorption tower. The dry method uses phosphine. The method of using solid oxidizer to remove phosphine or burning it directly is to mix and burn phosphine gas and air in the combustion furnace. The dry method among adsorption methods and chemical reaction methods has higher requirements on equipment technology and volume.
(Food and flour dosing)
2. Wastewater: At present, precipitation, coagulation, adsorption, ion exchange and biological methods are commonly used for phosphorus removal at home and abroad. Treating wastewater requires special wastewater treatment equipment and sites. If it cannot be operated continuously, it will have an impact on the wastewater treatment system or significantly increase the cost. At the same time, the amount of aluminum phosphide fumigation wastewater is small and scattered, and the huge wastewater treatment system cannot meet the requirements of flexible movement. Aluminum phosphide fumigation environmental plasticizer 168 wastewater treatment is relatively backward, and most of it is discharged to the warehouse sewage treatment system or naturally evaporates.
3. Waste:
A. Deep burial method: After fumigation and dispersion, collect the aluminum phosphide residue and immediately transport it to a secluded place 50m away from the water source, dig a pit and bury it deeply. This method is currently the main treatment method for aluminum phosphide residues. However, no anti-seepage measures have been taken, and the safety of buried residue cannot be guaranteed. If the residue encounters rainwater, phosphine gas will be produced. When the phosphine gas cannot be discharged, it will accumulate. In severe cases, it may cause poisoning of people and animals near the residue burial site or cause fire and smoke. This method is unscientific and cannot completely solve the hazards of aluminum phosphide residues.
(soaking pool)
B. Soaking method: Use washing powder, water, acid-base solution, etc. to soak the aluminum phosphide residue to promote the complete reaction of unreacted aluminum phosphide in the aluminum phosphide residue. This method can completely remove unreacted aluminum phosphide from the residue and completely solve the safety hazard. However, in actual operation, it was found that the immersion method will produce a large amount of phosphine. If the phosphine cannot be processed, it will pollute the surrounding air. In severe cases, accidents such as smoke and fire may occur.
C. Incineration method: The aluminum phosphide residue is incinerated at a temperature above 1100°C for reduction and harmless treatment. The residual ash after incineration can be used as an auxiliary material for cement production. This method requires the construction of a special incinerator. Since the amount of aluminum phosphide residue produced in each region is small, this method is expensive, and safety hazards when transporting aluminum phosphide residue cannot be avoided, so the operation is difficult.
(Incinerator)
Thoughts on scientific treatment of residues
1. Waste gas treatment countermeasures: Wet treatment in chemical reaction methods is relatively easy to implement and has great economic value. Calcium hypochlorite solution is used to oxidize phosphine to purify waste gas, and the treatment effect of dimethyl silicone emulsifier can reach 99% (this method is currently less feasible in grain depots).
2. Countermeasures for waste residue treatment: Aluminum phosphide reacts quickly with hot water at a higher temperature to generate phosphine and release it. The phosphine filtration and absorption device is used to purify and absorb the phosphine to achieve safety and Environmentally friendly and thorough treatment of aluminum phosphide residue, no phosphine gas and aluminum phosphide can be detected in the treated aluminum phosphide residue.
3. Wastewater treatment countermeasures: Due to the discontinuous production of aluminum phosphide fumigation wastewater and the small amount of water, biological methods cannot be used. Precipitation, coagulation, adsorption and ion exchange methods can be used for treatment. The designed wastewater treatment system must reduce volume and weight, be mobile, small in size, and have high treatment efficiency.
