Bittern, also called brine, generally refers to highly mineralized water. It often contains potassium ions, sodium ions, etc. In nature, there are many brine deposits, such as: salt lake brine, underground brine, and oil field brine. In industry, nitrate (NaNO3) is made from natural brine. However, the raw brine contains many impurities, say, calcium ions (Ca2+) and magnesium ions (Mg2+). Therefore, in the early stage of soda niter production, it is necessary to conduct a chemical reaction with sodium hydroxide (NaOH) and sodium carbonate (Na2Co3) to remove impurities and finally form calcium carbonate (CaCo3) and magnesium hydroxide (Mg(OH)2), which are insoluble and deposit. These sediments are first concentrated, and then mix with flocculants. This is how salt sludge is formed. After that, salt sludge is pumped into the plate and frame filter press for solid-liquid separation and brine recovery.
For calcium and magnesium salt mud, because of flocculant, the filter cakes are easier to form, so chamber filter presses can meet the dewatering demand. Because the filter plates are made of polypropylene and all contact parts are also PP, so the pp filter press is corrosion-resistant and widely used in the nitrates industry. If manufacturers have special requirements, the filter press structure can be clad by stainless steel for anti-corrosion. Regarding the filtration process of salt sludge, generally, it will pass in clean water to wash filter cakes. After cake washing, compressed air is introduced to remove the residual liquid in filter press chambers and cakes. The chamber type filter press is suitable for various salt mud with different calcium magnesium ratios. After filtration and dehydration, the cake moisture can be below 20%.