In domestic, municipal, and industrial wastewater, such as that from chemical nickel plating, anodizing, and phosphating processes, excess phosphorus is a common issue. If discharged untreated, it can lead to severe environmental problems like water eutrophication. The difficulty of treating various forms of phosphorus, such as organic phosphorus, orthophosphate, and condensed phosphates (pyro-, meta-, poly-, and hypophosphates), varies.
Phosphorus removers are chemical agents specifically designed to remove phosphorus from wastewater, particularly in industries like papermaking. These agents work by chemically converting soluble phosphates into insoluble precipitates, which can then be separated from the water, thereby reducing the risk of eutrophication. Below are several common phosphorus removers used in papermaking wastewater and their characteristics:
Iron Salts and Aluminum Salts Phosphorus Removers: These include agents like polyferric sulfate, ferric chloride, ferrous sulfate, aluminum sulfate, aluminum chloride, and polyaluminum chloride. The hydrolysis of these salts in water produces ferric hydroxide colloids with strong adsorption properties, capable of forming insoluble iron phosphate precipitates with phosphates, effectively removing phosphorus from wastewater. Iron salts are particularly effective for removing inorganic phosphorus and, under certain conditions, can also remove some organic phosphorus.
Calcium Salt Phosphorus Removers: Examples include lime (calcium hydroxide) and calcium chloride. These work by raising the pH of the water, prompting the formation of insoluble calcium phosphate precipitates with phosphates. This method is suitable when pH adjustment is also required, but its removal efficiency and applicability may not be as extensive as those of iron and aluminum salts.
Composite Phosphorus Removers: To improve phosphorus removal efficiency and adapt to a wider range of water quality conditions, composite phosphorus removers are sometimes used. These may contain multiple components such as iron, aluminum, and calcium, or specially modified single salts, enhancing their ability to remove different types of phosphorus, including hard-to-treat hypophosphites.
Hypophosphite Removers: Specifically designed for the removal of hypophosphites, these typically involve multiphase inorganic composite salts that can form stable coordination bonds with hypophosphite ions under acidic conditions, leading to precipitation. This is particularly applicable in industrial wastewater from chemical nickel plating, anodizing, and similar processes.
When choosing a phosphorus remover, factors to consider include the specific characteristics of the wastewater, the form of phosphorus present (inorganic or organic), treatment costs, and compatibility with existing treatment facilities. Typically, to achieve better phosphorus removal, the use of phosphorus removers may need to be combined with other treatment technologies, such as coagulation, sedimentation, and filtration.
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