Water treatment agents refer to chemical reagents used for water treatment, typically for sewage treatment. They are widely applied in industries such as chemical engineering, petroleum, light industry, daily chemicals, textiles, printing and dyeing, construction, metallurgy, machinery, medicine and health, transportation, and urban-rural environmental protection, aiming to save water and prevent water source pollution. These agents are used in technologies including cooling water and boiler water treatment, seawater desalination, membrane separation, biological treatment, flocculation, and ion exchange, encompassing corrosion inhibitors, scale inhibitors and dispersants, biocides and algaecides, flocculants, ion exchange resins, purifiers, cleaning agents, and prefilming agents.
Therefore, it is necessary to avoid antagonistic effects caused by inappropriate compounding of components, which may reduce or eliminate efficacy, while fully utilizing the synergistic effect (enhanced efficacy when multiple agents coexist). Additionally, most water treatment systems are open systems with certain discharge volumes, so the environmental impact of various water treatment agents must be considered during use.
Corrosion inhibitors are chemicals that, when added to water at appropriate concentrations and forms, prevent or slow down corrosion of metal materials or equipment by water. They feature high efficiency, low dosage, and convenient use.
- By compound type: Inorganic inhibitors (e.g., chromates, nitrites, molybdates) and organic inhibitors (e.g., amines).
- By inhibition mechanism: Anodic inhibitors, cathodic inhibitors, or mixed inhibitors.
- By protective film formation mechanism:
- Passivation film type: Chromates, nitrites, molybdates (common in water treatment).
- Precipitation film type: Polyphosphates, zinc salts.
- Adsorption film type: Organic amines.
Scale inhibitors, also known as antiscalants, are chemicals that inhibit the formation of scale from calcium, magnesium, and other scaling salts in water. They include:
- Natural inhibitors: Tannins, lignin derivatives.
- Inorganic inhibitors: Sodium hexametaphosphate, sodium tripolyphosphate.
- Organic and polymeric inhibitors (most effective and promising):
- Organic phosphonic acids: EDTMP (Ethylenediaminetetramethylene Phosphonic Acid), HEDP (Hydroxyethylidene Diphosphonic Acid).
- Polycarboxylic acids: Polyacrylates, hydrolyzed polymaleic anhydride.
Their scale inhibition mechanisms typically involve lattice distortion and dispersion-condensation, widely used in oilfield water, boiler water, and industrial cooling water systems.
Biocides, also known as algaecides, sludge stripping agents, or anti-sludge agents, suppress the growth of microorganisms like bacteria and algae in water to prevent microbial slime formation. They are categorized into:
- Oxidizing biocides: Chlorine, sodium hypochlorite, bleaching powder.
- Non-oxidizing biocides: Chemicals that damage bacterial cell walls and cytoplasm, such as quaternary ammonium salts (e.g., dodecyl dimethyl benzyl ammonium chloride or bromide), which often have multiple functions (sterilization, stripping, corrosion inhibition) and are widely used in oilfield water and industrial cooling water.
Flocculants remove or reduce turbidity/suspended solids in water and accelerate sedimentation of impurities and sludge. Early applications included inorganic flocculants (e.g., alum, ferric chloride). Organic and polymeric flocculants are increasingly used in water and wastewater treatment, classified as:
- Anionic flocculants: Carboxymethyl cellulose, sodium polyacrylate.
- Cationic flocculants: Polyethylene amine.
- Non-ionic flocculants: Polyacrylamide.
Their flocculation relies on charge neutralization and adsorption bridging.
Purifiers are specialized chemicals for oilfield water treatment, removing mechanical impurities and oil from oily wastewater. Besides separating suspended solids/mechanical impurities like general flocculants, they also facilitate oil-water separation. They often contain surfactants in addition to flocculant components (e.g., aluminum salts, polyacrylamide). Purification efficiency is measured by a membrane filter, expressed as the membrane factor.
Cleaning agents are chemicals used to remove deposits (e.g., corrosion products, scale, microbial slime) from metal equipment surfaces during water treatment pretreatment. They include:
- Acid cleaners: Hydrochloric acid, sulfuric acid, hydrofluoric acid, citric acid.
- Passivators: Sodium benzoate.
- Surfactant cleaners: Sodium bis(α-ethylhexyl) sulfosuccinate, for removing oil and rust.
Prefilming agents form a protective film on metal surfaces during water treatment pretreatment, serving two purposes:
- Increasing the initial dosage of corrosion inhibitors to enhance efficacy.
- Enabling maintenance and repair of the film with low-dose inhibitors, saving costs.
Common prefilming agents include sodium hexametaphosphate with zinc salts and sodium tripolyphosphate.
简体中文
English
