Precipitation processes are commonly used in the mining industry to recover precious metals such as silver, gold, and zinc from ores. While these processes are effective in separating the metals from the impurities, they also generate a significant amount of waste in the form of precipitates. To avoid environmental contamination, it is essential to filter these precipitates before disposal.
One of the most popular filtration techniques for precipitates is the plate and frame filter press. This equipment consists of a series of filter plates and frames that are arranged alternately, and a set of hydraulic cylinders that are used to apply pressure to the plates. The precipitate slurry is fed into the centre of the press, and the liquid is forced through the filter cloth on the plates, leaving behind a cake of solid material.
Plate and frame filters are preferred for precious metal filtration due to their low cost, great strength, and ease of cleaning and maintenance. Unlike other filtration systems, plate and frame filters allow for easy inspection of the internal components, which is crucial for identifying and addressing any problems that may arise during operation.
Additionally, plate and frame filters are highly customizable, and can be made in every conceivable combination of inlet and outlet positions. This allows for greater flexibility in designing a filtration system that best suits the specific needs of the application.
For precious metal filtration, bottom inlet and top outlet positions are considered best for precoating and filter aid suspension. Larger filters may require inlets and outlets to be located at opposite ends of the filter for optimal performance. It is also essential to purge any air from the filter before precoating is completed, which can be challenging if gasketed filter septa are used.
Polypropylene filter plates are the preferred choice for plate and frame filters in precious metal filtration due to their low cost, excellent chemical resistance, and durability. Polypropylene recessed filter plates and gasketed filter cloth are commonly used in plate and frame filters to ensure the highest quality filtration.
The capacity of plate and frame filters varies from 0.6 cubic feet to 6 cubic feet, depending on the size of the application. The filters are made of mild steel construction, and the head and tail plates are Blanchard ground to ensure flatness. An articulating coupling at the tail plate to hydraulic cylinder rod connection ensures smoother operation, while a centre feed with four corner discharge allows for even distribution of the precipitate slurry.
Closure for plate and frame filters is achieved through a two-stage automatic air and oil hydraulic pump, and opening is accomplished through an automatic, spring-assisted mechanism. A hydraulic pump, pressure gauge, and air blow-down header with valves are included for optimal operation.
Optional features for plate and frame filters include a sludge hopper for collecting and discharging the filtered solids, and an elevated frame for easier maintenance and cleaning.
In conclusion, plate and frame filter presses are an excellent low-cost solution for precious metal filtration. With their versatility, ease of maintenance, and customizable options, they are the preferred choice for many applications in the mining industry. Polypropylene filter plates ensure reliable and efficient filtration, making plate and frame filters an essential piece of equipment in the precious metal refining process.