Adding diatomite filter aid during filtration is similar to precoating. The diatomite is first mixed into suspension of a certain concentration (generally 1∶8 ~ 1∶10) in the mixing tank, and then the suspension is pumped into the liquid main pipe according to a certain stroke by the metering adding pump and mixed evenly with the titanium liquid to be filtered before entering the filter press. In this way, the added diatomite filter aid is evenly mixed with the suspended solid and colloidal impurities in the filter titanium solution and deposited on the outer surface of the precoating or filter cake, continuously forming a new filter layer, so that the filter cake always keeps good filtration performance. The new filter layer not only has the ability to capture suspended solids and colloidal impurities in the titanium liquid, but also allows the clear liquid to pass through the labyrinth of microporous channels, so that the filtration can be carried out smoothly. The amount of diatomite filter aid depends on the turbidity of titanium solution to be filtered. The turbidity of different batches of liquid titanium is different, and the turbidity of the upper and lower parts of liquid titanium in the same tank is also different. Therefore, the stroke of the metering pump should be flexibly mastered, and the amount of diatomite filter aid should be adjusted.
Studies have shown that different amount of diatomite filter aid has great influence on the increase rate of pressure drop and the length of the whole filtration cycle of the same titanium liquid filtration. When the amount is insufficient, the pressure drop increases rapidly from the start, greatly shortening the filtration cycle. When the amount of added is too much, at the beginning of the pressure drop increase speed is slow, but later because the filter aid quickly filled the filter chamber of the filter press, there is no space to accommodate new solids, the pressure drop rapidly increased, the flow sharply decreased, forcing the pressure filter process to stop, so that the pressure filter cycle is shortened. The longest filtration cycle and maximum filtration yield can be obtained only when the adding amount is appropriate, the pressure drop rises at a moderate rate and the filter cavity is filled at a moderate rate. The most suitable amount of addition is summed up through the condition test in production practice, can not be generalized.
Under the same filtration conditions, the consumption of diatomite filter aid is greatly reduced than that of charcoal powder filter aid, and the cost is reduced. Using diatomite instead of charcoal powder is beneficial to exploit the rich diatomite resources in China, protect the limited forest resources, and realize the harmonious unity of economic development and environmental protection.