(/), my country's water pollution problem with heavy metals is very prominent. Heavy metal wastewater mainly comes from electroplating, mechanical processing, mining, steel and non-ferrous metal smelting and some chemical enterprises. Due to the non-degradability of heavy metals in the environment and their harm to humans and the environment, heavy metal wastewater treatment must meet standards.
In order to make the heavy metals contained in sewage meet the water quality requirements for drainage of a certain water body or reuse, it is the process of purifying it. At present, heavy metal wastewater treatment methods can be roughly divided into three categories: (1) chemical methods; (2) physical treatment methods; (3) biological treatment methods.
Heavy metal wastewater is one of the most serious industrial wastewaters that pollutes the environment and is most harmful to humans. The Japanese pollution diseases that shocked the world in the 1960s, Minamata disease and Itai-itai disease, were caused by mercury-containing wastewater and cadmium-containing wastewater polluting the environment respectively. Therefore, all countries attach great importance to the treatment of heavy metal wastewater.
Treatment characteristics and basic principles Heavy metals in wastewater cannot be decomposed and destroyed by various common methods, but can only transfer their location and transform their physical and chemical forms. For example, after chemical precipitation treatment, the heavy metals in the wastewater change from the dissolved ion state to insoluble compounds and precipitate, and are transferred from the water to the sludge; after the ion exchange treatment, the metal ions in the wastewater are transferred to the ion exchange resin on; after regeneration, it is transferred from the ion exchange resin to the regeneration waste liquid. In short, heavy metal wastewater forms two products after treatment, one is treated water with heavy metals basically removed, and the other is concentrated products of heavy metals. Treated water with a heavy metal concentration lower than the discharge standard can be discharged; if it meets the production process water requirements, it is best to reuse it. Most of the heavy metals in the concentrated products have use value and should be recycled as much as possible; those with no recycling value should be treated harmlessly.
Problems with heavy metal wastewater treatment in my country: Currently, the treatment process used in heavy metal-containing wastewater basically uses the treatment process provided by Japan. It is mainly composed of a sulfidation treatment process, a gypsum neutralization process, and an iron salt oxidation process. Although this combined process can make the treated water discharge up to standard, it also has the following shortcomings: 1. A large amount of sludge containing hydrogen sulfide gas is produced during this process. In order to ensure the removal rate of heavy metals, excessive sulfide is often added. Excessive sulfide will generate hydrogen sulfide gas under acidic conditions. Hydrogen sulfide gas is highly toxic and can easily cause personal injury to on-site personnel; 2. The heavy metal sulfide generated is very fine and the sludge particles are fine, making dehydration difficult; 3. The sludge contains a large amount of arsenic, copper and other heavy metal ions. If the sludge residue cannot be processed in time, leaching will occur and the heavy metals will seep into the groundwater, causing secondary pollution problems; 4. The amount of raw materials and slag is very large, causing material transportation Difficulties, the limestone pretreatment equipment is huge and covers a large area; 5. The generated gypsum is not strong enough and contains toxic substances such as heavy metals, making the gypsum difficult to use, resulting in a waste of resources; 6. The effluent is highly salty sewage and cannot be reused , affecting the total recycling rate of wastewater; 7. The water treatment facilities and equipment are huge, and the combined water treatment system is very large and complicated.
Future development direction: 1. The process flow is relatively simple and the construction cost is low. Hydrogen sulfide gas cannot be produced during the treatment process, and personnel safety is better; 2. The treated water quality can be reused; 3. There are Valuable metal recycling; 4. Wastewater treatment has low cost, high efficiency, easy management, no secondary pollution, and is conducive to the improvement of the ecological environment.