What is Chemical Waste?

Waste in chemical terms refers to the emissions that are generated in chemical experiments and that have basically or completely lost their use value within a certain time and space and cannot be recycled and utilized. Chemical waste can be divided into three types according to physical form: waste gas, waste liquid and waste residue, referred to as "three wastes".

Chemical waste can be divided into three types according to physical form: waste gas, waste liquid and waste residue, referred to as "three wastes".

1. Exhaust gas, also called gaseous waste, mainly refers to the volatiles of reagents and samples, the exhaust gas generated when using instruments to analyze samples, the toxic and harmful gases generated during the experiment, and the leaked and evacuated standard and carrier gases. For example: acid mist, formaldehyde, benzene series, various organic solvents, mercury vapor, phosgene, etc.

2. Waste liquid, also called liquid waste, mainly refers to excess samples, residual liquid after the experiment, standard curve and sample analysis residual liquid, invalid storage liquid and washing liquid, experimental container washing liquid, etc. Divided into inorganic waste liquid and organic waste liquid, inorganic waste liquid contains heavy metals (such as iron, cobalt, copper, manganese, cadmium, lead, gallium, chromium, titanium, germanium, tin, aluminum, magnesium, nickel, zinc, silver, cyanide (Free cyanide, cyanide or complex cyanide), mercury (Hg ⁺ or Hg ²⁺ ), fluorine (fluoric acid or fluoride), acid or alkali, hexavalent chromium, etc .; organic waste liquids include greases (such as lamp oil , Light oil, turpentine, paint, creosote oil, spindle oil, insulating grease, lubricating oil, heavy oil, cutting oil, cooling oil, animal and vegetable oil, etc., halogen-containing organic solvents (such as chloroform, methyl chloride, Aliphatic halogen compounds such as methyl chloride, tetrachlorocarbon, methyl iodide, or aromatic halogen compounds such as chlorobenzene, benzyl chloride, and polychlorinated biphenyls), halogen-free organic solvents (such as phenols, ethers, nitrates Benzenes, anilines, organophosphorus compounds, petroleum, etc.).

3. Waste residue, also called solid waste, mainly refers to excess samples, synthesis and analysis products, expired or expired chemical reagents, consumed or damaged experimental supplies (such as glassware, gauze), etc.

According to the National Catalogue of Hazardous Wastes (Order of the Ministry of Environmental Protection [2008] No. 1), chemical wastes can be classified into hazardous wastes and non-hazardous wastes according to their hazards. Hazardous waste refers to chemical waste with one or more hazardous properties such as flammability, corrosiveness, toxicity, and reactivity. It also includes exclusion of hazardous properties, but may cause harmful effects on the environment or human health. Chemical waste managed as hazardous waste.

Flammable wastes: solid wastes with a ignition point below 60 ° C, which have a tendency to catch fire due to friction or moisture absorption and spontaneous changes; wastes that burn violently and continuously during a fire, and can cause combustion danger during management

Corrosive waste: including wastes that cause damage to the cell tissues of biological contact sites, or have significant corrosive effects on loading containers; water-containing wastes, or the pH of the leachate of which does not contain water but is added with quantitative water, 12.5 or 2 Waste; when the minimum temperature is below 55 ° C, the annual corrosion depth of steel products is greater than 0.64cm.

Toxic waste: including compounds containing mercury, lead, cadmium, chromium, copper, zinc, arsenic, cyanide, asbestos, organic chlorine solvents, etc.

Reactive waste: including strong acid, strong alkali, strong oxidant, strong reducing agent, etc. ^[1]

1. The main harms to the human body are allergies, causing irritation, hypoxia, coma and anesthesia, poisoning, carcinogenic, teratogenic, mutagenic, pneumoconiosis, etc. Certain chemical wastes in direct contact with the skin can cause the skin protection layer to fall off, causing dry, rough, painful, and even dermatitis skin; contact with the eyes can cause minor injuries, temporary discomfort, and even permanent disability. For example: Chronic inhalation of benzene in the human body can cause headache, dizziness, fatigue, paleness, vision loss and balance imbalance; liquid benzene in contact with the skin can dissolve the sebum of the skin and dry the skin; high concentration of benzene vapor has mild irritation to the eyes And produce blisters. Some chemical waste, such as heavy metal elements, may not show symptoms of damage for a long time after entering the human body, but the potential harm is extremely great. For example: In the 1950s, a chemical plant in Japan discharged wastewater containing methylmercury into the sea, contaminating marine life, and local residents consuming fish with high concentrations of organic mercury for a long time, causing mercury poisoning, movement disorders, and extremities. The symptoms of numbness, pain, and teratosis killed about 1246 people.

2. The harm to the environment not only directly pollutes the environment, but also some chemical waste in the environment through chemical or biological transformation to form secondary pollution, the harm is greater. If the waste is discharged into the atmosphere, it can cause air pollution and affect human health, industry, agriculture, weather and climate. For example, a large amount of sulfur oxides or nitrogen oxides are discharged into the atmosphere, which will form acid rain and directly affect the normality of animals and plants. If the waste is discharged into the water body, it can cause water pollution and threaten the survival of aquatic life. For example, when the cyanide concentration in the water reaches 0.5mg / L, the fish will be destroyed within 2h. 20% of deaths, all within one day; if the waste is discharged into the soil, it can cause changes in the composition and structure of the soil, affect the microbial activity in the soil, contaminate the plants growing in the soil, and even fail to cultivate, for example: The soil near the metallurgical plant is polluted by non-ferrous smelting slag. Plants growing in the soil contain 20 to 80 times the zinc content, 80 to 260 times the lead content, and 30 to 50 times the copper content. ^[1]

(1) Incineration method. Combustible waste liquid can be burned in a combustion furnace. If the amount is small, you can choose a safe place for outdoor combustion. For difficult-to-burn waste liquid, you can mix it with combustible materials or spray it into an incinerator equipped with a burner. Medium combustion; for waste liquids that can produce harmful gases such as nitrogen dioxide, sulfur dioxide, hydrogen chloride, etc., they can be burned with an incinerator equipped with a scrubber, or the combustion waste gas can be washed with an alkaline solution to remove harmful gases; the waste residue can be dissolved in Combustion in flammable solvents.

(2) Adsorption method. Adsorbents such as activated carbon, diatomaceous earth, alumina, layered fabric, polypropylene, polyester flakes, urethane foam plastic, straw shavings, sawdust, etc. are used to fully adsorb harmful components, and then burned with the adsorbent.

(3) Solvent extraction method. For water-containing low-concentration waste liquid, it can be extracted with volatile solvents such as n-hexane that are immiscible with water, and the solvent is separated and burned.

(4) Distillation. Harmful components are removed by distillation or fractional distillation using the different boiling points of the components in the waste liquid.

(5) Neutralization method. The pH value is adjusted to neutral through acid-base neutralization reaction.

(6) Precipitation method. Add a suitable precipitating agent and control the temperature, pH value and other conditions, so that the harmful ingredients will form a precipitate or polymer with little solubility.

(7) Hydrolysis method. For organic or inorganic acid esters, some organic phosphorus compounds and other easily hydrolysable substances, sodium hydroxide or calcium hydroxide can be added and hydrolyzed at room temperature or under heating. If the hydrolysate is not harmful, it can be discharged after neutralization and dilution; if the hydrolysate is harmful, it can be treated by appropriate methods such as adsorption and then discharged.

(8) Oxidation method. Add appropriate oxidants, such as ozone, chlorine-containing compounds, etc., to convert harmful components into harmless or less harmful substances.

(9) Reduction method. For heavy metals, suitable reducing agents such as iron filings, copper filings, ferrous sulfate, sodium bisulfite, and sodium borohydride can be added to convert them into a form that can be easily separated and removed. ^[1]