The toxicity of several drugs used in the first section of chemical cleaning
(1) Hydrochloric acid:
The aqueous solution of hydrogen chloride is hydrochloric acid. Hydrogen chloride Hcl is a colorless gas with a strong odor, a boiling point of -85 ° C, a melting point of -110 ° C, a density of 1.3, slightly heavier than air. Hydrogen chloride forms white hydrochloric acid fumes in the air and is highly soluble in water. The content of hydrogen chloride in industrial hydrochloric acid is generally not less than 27%, usually 31%, and hydrogen chloride gas escapes at room temperature. Industrial hydrochloric acid has the best quality of synthetic acid. Hydrochloric acid recovered in other industries, although cheap, generally contains more impurities, such as metal ions such as iron, lead, and arsenic. When using this acid, it is necessary to carry out a rigorous analysis of the ingredients, and only when the content of all harmful impurities does not exceed the national standard (or emission standard).
The cause of the hazard caused by hydrochloric acid is mainly caused by the action of hydrogen chloride and water vapor in the air to produce hydrochloric acid fumes. It has a strong stimulating effect on the upper respiratory tract and is also corrosive. When concentrated hydrochloric acid is diluted to a lower concentration, there is almost no obvious hazard, and the irritation and corrosivity are small, which is safe for the human body. Wear masks and rubber gloves when handling concentrated hydrochloric acid to avoid contact with skin or splashing into eyes. When concentrated hydrochloric acid is in contact with the skin, rinse with water for 1-2 minutes, then rinse with 2 to 3% sodium bicarbonate (NaHCO3) solution. In case of splashing into the eyes, it must be washed immediately with a large amount of water (preferably distilled water), and then washed with 0.5% sodium carbonate solution. In severe cases, it should be sent to the hospital for treatment.
(2) Sodium hydroxide:
Sodium hydroxide (NaOH), also known as caustic soda, caustic soda or caustic soda, white solid, melting point 318.4 ° C, boiling point 1390 ° C, solubility in water at 0 ° C is 42%, with strong water absorption. Sodium hydroxide can dissolve proteins to form basic protein compounds, which have obvious corrosive effects on human tissues. Because of its lysis of proteins, especially on the mucous membranes, it can form a "soft palate" that does not prevent the lye from entering the tissue deeper, so it can cause burns when it comes into contact with the skin. The higher the concentration of the alkali solution, the higher the temperature, the stronger the burnability. Even a very small amount of sodium hydroxide enters the eye. It is dangerous because the lye quickly enters the inside, which not only damages the surface part of the eye (such as corneal opacity), but also penetrates inside to damage the iris. Be careful when using it. In case of splashing on the skin or in the eyes, rinse immediately with water or rinse with boric acid. In severe cases, it should be sent to hospital for treatment.
The use of NaOH should not be negligent due to its being a solid. When opening the caustic soda bucket, you must wear overalls, rubber gloves and safety glasses, and use special tools. When breaking large pieces of caustic soda, wrap it in a waste cloth or in a vat without a lid. To prevent the splash of pieces. When transporting a container containing a concentrated solution of caustic soda, a special car is used. Under no circumstances should the container be placed on the shoulder or carried in the arms.
(3) Sodium nitrite:
Sodium nitrite (NaNO2) is a colorless rhombic prism crystal with a melting point of 276.9 ° C. It is easily soluble in water, and its aqueous solution releases oxynitride (yellow smoke) when it is acid.
Sodium nitrite does not exhibit strong acute damage to human tissues, unless a certain amount of ingestion can cause vasodilation, rapid pulse, and lower blood pressure.
The toxicity of sodium nitrite is that it can produce carcinogenic nitrosamines under certain conditions (such as in the digestive tract) when it encounters secondary amine compounds, which is the main reason for strict control of sodium nitrite emission concentration in environmental protection.
When sodium nitrite is used as a passivating agent, the procedure can be carried out according to the general chemical operating procedures. However, it is strictly forbidden to discharge directly without any treatment, and it is not allowed to contact the waste liquid with the acid solution. Otherwise, the release of nitrogen oxides can seriously pollute the environment.
(4) Trisodium phosphate:
Trisodium phosphate, sodium phosphate, usually contains 12 crystal waters (Na3PO4•12H2O) to become colorless crystals. It has a specific gravity of 1.62 and a melting point of 73.4 ° C. It is weathered in dry air. When heated to 100 ° C, the water of crystallization is lost and becomes an anhydrate. Trisodium phosphate is dissolved in water, and is almost completely decomposed into disodium hydrogen phosphate and sodium hydroxide in an aqueous solution, and the solution is alkaline.
The toxicity of trisodium phosphate can only occur when the dose is very high. Under the passivation condition, the toxicity of the drug does not need special attention, and it can be required according to the operation requirements of general chemicals.
(5) Sodium carbonate:
Sodium carbonate (Na2CO3) is a white powder with a specific gravity of 2.532 and a melting point of 851 ° C. It is commonly known as soda ash or soda. Sodium carbonate is easily soluble in water, and the aqueous solution is strongly alkaline, and it is easy to absorb water and carbon dioxide in the air to form sodium hydrogencarbonate. Sodium carbonate is a non-toxic chemical and has no special requirements when used.
(6) Corrosion inhibitor:
Corrosion inhibitors vary widely in toxicity depending on the variety selected. Corresponding safety measures should be developed according to the specific situation. For example, when using 02 corrosion inhibitors, since aniline and formaldehyde are highly toxic substances, extremely strict operating procedures and waste liquid treatment measures must be specified to ensure the least possible harm to operators and the environment. If a safer corrosion inhibitor is used, there is no need to make special provisions for the use process and waste discharge.
Section 2 Safety Measures in Chemical Cleaning Engineering
(1) Before the chemical cleaning, the boiler must be strictly inspected. If the boiler heat exchange tube is found to have severe local corrosion (small hole corrosion, ulcer corrosion) and any form of cracking or bubbling, these parts must be taken. Switch it before you can clean it.
(2) The installation of temporary pipelines must be strictly guaranteed. After the installation, the hydraulic pressure test must be carried out. For any small seepage or leakage, it must be re-welded until it is fully qualified.
(3) The highest part of the chemical cleaning system should be installed with an exhaust outlet to prevent the harm of hydrogen caused by iron corrosion due to poor corrosion inhibitor effect or improper use. At the same time, after the highest part is deflated, the entire cleaning system can be filled with cleaning medium without leaving a dead angle.
(4) The cleaning site must have sufficient lighting and smooth roads. The power supply and the lighting power supply are separated, and the power control panel is placed far away from the cleaning system, and is convenient to operate.
(5) Prepare necessary emergency medicines and labor protection supplies. First-aid medicines generally have the following types: 2 to 3% sodium bicarbonate and sodium carbonate solution; saturated lime water; 1-2% boric acid aqueous solution; 1-2% acetic acid or hydrochloric acid aqueous solution; distilled water. Labor insurance products include: rubber gloves, aprons; protective eyes; overalls; towels; cotton wool;
(6) The operation must be unified and the division of labor is responsible. All important parts (such as acid pump, valve, dosing point) must be set up on duty. The duty officer must strictly observe the position and obey the command.
(7) No open flames (such as electric welding, smoking, heating, etc.) should be used at the chemical cleaning site. In case of fire and other accidents.
(8) A special lounge must be set up at the cleaning site for non-on-duty personnel to rest, and it is not allowed to sleep and rest next to the pickling system. Drinking water and food should be placed in the lounge and should not be mixed with chemicals to avoid ingestion.
(9) Each chemical operation step must be carried out in strict accordance with the operating procedures and requirements, and the operating procedures should not be changed arbitrarily. In particular, it is strictly forbidden to manually hold the acid bottle and add acid directly to the boiler. This will cause the acid solution to splash out with the large amount of gas (carbon dioxide), causing personal accidents.
Section 3 Waste Treatment and Discharge in Chemical Cleaning Process
The standards for waste discharge must be implemented in accordance with the waste discharge standards stipulated by the state. The alkali wash, pickling solution and passivation solution exceeding the discharge standard should be post-treated accordingly. The treated solution meets the national discharge standards. After that, it can be discharged. For small and medium boiler chemical cleaning processes, the post-treatment method is generally dilution and neutralization. When a particularly toxic cleaning, corrosion inhibitor or passivating agent is selected, special post-treatment must be applied to the selected material before the waste liquid can be discharged.
The dilution method is mainly applicable to general acid and alkali cleaning solutions with low concentration. When the hydrochloric acid and sodium carbonate or sodium hydroxide or trisodium phosphate solution are not discharged from the boiler, they are diluted with a larger amount of water, so that the pH of the waste liquid entering the sewage pipe after mixing is 6-9. The suspended matter is less than 500 mg / liter, so that the discharged waste liquid basically conforms to the national standard. Of course, this method is not suitable for the discharge of higher concentration acid and alkali cleaning liquids because it requires too much water to be consumed. For such effluent, appropriate neutralization should be done before dilution.
The neutralization method is mainly applicable to higher concentrations of hydrochloric acid and sodium hydroxide effluent. If the effluent is hydrochloric acid, it is neutralized with caustic soda or lime. If it is alkali, it is neutralized with hydrochloric acid, neutralized to a pH of 7 to 9, and then discharged after appropriate dilution. This method requires a little acid or alkali, but the cost is not high, and it is easier to meet the emission standards. The specific operation is to discharge the waste liquid into a transition pit first, and the waste liquid is added to the treatment agent at the same time as the waste liquid enters the pit. The speed of the medicine addition is just enough to ensure that the waste liquid discharged from the transition pit meets the waste liquid discharge standard. If the caustic wash effluent and the pickling effluent are just mutually neutralized acids and bases, and conditionally store the lye discharged first, then the alkali wash and the pickling waste are neutralized with each other, saving And the raw materials consumed are feasible.
It must be noted that not all acid and alkali solutions can be treated by neutralization. For example, after the treatment of hydrofluoric acid effluent, it not only considers that the pH of the effluent reaches the standard, but also must consider that the concentration of F- can not exceed the emission standards stipulated by the state. Therefore, for the treatment of hydrofluoric acid waste liquid, only the lime neutralization method can be used, and the pH of the discharge liquid can be increased to 6 to 9, and the concentration of the free F-ion to be less than 10 mg/liter can be discharged. The amount of lime is generally not less than twice the amount of pure hydrofluoric acid.
In the small and medium-sized boiler cleaning process, the passivation solution is generally made of trisodium phosphate solution. After the passivation, the waste liquid is treated according to the alkali substance, and the neutralization method can be used. If the sodium nitrite is used for passivation, then passivation The liquid must be subjected to special chemical treatment measures. Ensure that the residual concentration of NaNO2 meets emission requirements. There is no mature method for the treatment of sodium nitrite. It is a good method to decompose urea with acid in an acidic medium. Controlling the pH is the key to complete the above reaction. This chemical is carried out in densely populated areas. Before the treatment, sufficient small experiments must be carried out to enable the operators to fully master the process conditions before they can carry out industrial chemical treatment. We believe that the passivation of small and medium-sized boilers is preferably phosphate, and nitrite is only used when special requirements are required.
High Power Underwater Spot Light
High Power Underwater Spot Light,Led Inground Underwater Pool Light,Outdoor Waterproof Underwater Spot Light,Garden Underwater Led Spot Light
Shenzhen Poolux Lighting Co., Ltd. , https://www.pooluxled.com