Methods for manufacturing PAC
Manufacturing methods for poly aluminum chloride (PAC) can vary; according to raw materials, they can be classified into methods involving aluminum, active alumina, aluminum oxide, aluminum chloride, and alkaline solution.
①Aluminum Method. Using this method, PAC is synthesized using byproducts from aluminum processing, such as aluminum shavings, ash, and slag, among others. The aluminum ash reacts with hydrochloric acid at a certain ratio under stirring to produce liquid PAC with subsequent dilution, filtration, concentration, and drying. The process can be divided into acid, alkali, and neutralization methods. Acid method mainly uses HCl, making product quality difficult to control; the alkali method is more complex, requires larger equipment investment, and consumes more alkali, making pH value control costly and material consumption high; the most commonly used method is the neutralization method, which can generally meet national standards if the ratio is controlled well.
②Alumina Method. This method involves heating and pressurizing alumina powder to dissolve it in acid, producing PAC with low levels of toxic substances like heavy metals. This process is simple but produces PAC with a lower degree of basicity, so it usually involves two processes: heating and pressurizing alumina and neutralizing it with calcium aluminates.
③Aluminum Oxide Method. Raw materials containing aluminum oxide include bauxite, vanadium aluminum ore, kaolin, coal gangue, etc. Production a two-step process: first obtaining crystalline aluminum chloride, then through thermolysis or neutralization acquire polyaluminum chloride.
④Chlorine Aluminum Method. This method uses aluminum chloride powder as the primary raw material to process PAC, which is the most commonly applied method. Crystalline aluminum chloride can be thermolyzed at 170 degrees Celsius, then mixed with water to produce PAC, followed by solidification and drying.
⑤Alkaline Solvent Method. This method involves reacting aluminum ash with sodium hydroxide to obtain sodium aluminate solution, then adjusting the pH value with hydrochloric acid to produce PAC solution. This method produces a better color and appearance, fewer insoluble substances, but higher sodium chloride content, higher raw material consumption, and lower alumina content in the solution, resulting in higher production costs.