There are many equipment options available for washing, so when considering the correct equipment and process flow for your application, you must first take into account the type of contamination you wish to remove and the properties of the waste material.
Is the contaminate a tough, fine-grained, tacky clay that needs the aggressive scrubbing action of a Log Washer? Or is the contaminate a lighter, loamy type clay or dirt and dust that can be removed with either a Coarse Material Screw Washer or a Rotary Scrubber? Once this has been determined, then the proper equipment for the application can be selected based on feed size and capacity, among other variables that need to be considered.
McLanahan’s history of building rotary equipment and Log Washers dates back more than 100 years, and throughout this time, a large application database has been developed. Let’s take a look at one of McLanahan’s many wet processing machines, the Rotary Scrubber, and its use and application in your washing circuit. 
An aerial view of a McLanahan Rotary Scrubber.
What is a Rotary Scrubber?
Rotary Scrubbers are often used following primary crushing and typically for the removal of light, loamy type clays and similar soluble deleterious materials from feedstock with typical sizes of up to 12” (300mm). If the feed includes a tough, fine-grained, tacky clay, then consideration should be given to a Log Washer. The reason for this is because the tumbling action of the Rotary Scrubber drum turns small tacky clay balls into larger clay balls as they exit the drum.
Usually, the determining factors when selecting a Rotary Scrubber over other types of washing equipment are that it can accept larger feed sizes and that it is capable of high capacities in comparison to Log Washers or Coarse Material Screw Washers.
How they work
It is preferable that the –0.25” (6mm) fines fraction be removed from the feed before being introduced to the scrubber. This can be accomplished through traditional screening methods or by adding a desanding section to the scrubber to help remove a portion of the fines. By doing so, you are allowing the scrubbing action to be more vigorous as opposed to the fines fraction cushioning the scrubbing action.
The basic operation of a Rotary Scrubber. Fresh water and the material to be cleaned are introduced through the feed chute. As the cylinder revolves, the tumbling action and cascading of the aggregate on itself and on the liners break down the softer material and dissolve dirt, loam and other soluble material into the solution. This material can then be removed by a Dewatering Screen.
The feed solids and water are introduced in the feed chute of the Rotary Scrubber. The rotating drum (which is provided with lifter bars), in conjunction with centrifugal force, carries the slurried material up the side of the drum until approximately the 11 o’clock position, where it releases, cascades and tumbles back down to the cylinder bottom, where the process begins again. This process continues as the slurry is carried the length of the cylinder. The action helps break down softer materials and dissolve the dirt, loam and other foreign materials into a solution.
Feed material is continuously lifted and dropped by the tumbling action of the cylinder.
It is highly recommended that lab test work be performed on the feed material since each application differs and the selection and retention time necessary to achieve the desired level of cleanliness needs to be evaluated. In some instances, an adjustable weir at the cylinder’s discharge end can be provided to help with achieving the necessary retention time.
An adjustable weir can help provide the necessary retention time.
As the slurry exits the Rotary Scrubber, it is recommended that the material pass across a rinse or sizing screen. In certain applications, the Rotary Scrubber can be supplied with a trommel screen extension and an internal spray bar for making a rough sizing cut. This extension can be either a single- or double-shell design to allow for the creation of multiple product-size cuts. This screen media can be made from abrasion-resistant, perforated rolled plate, rubber or urethane screen panels. Depending on the cut point and capacity, a trommel extension may not be suited for an accurate product separation. Capacities of up to 2,500 tph can be achieved in a single Rotary Scrubber.
Once this process has been completed, the washed product is ready for further downstream crushing or sizing.
If a Rotary Scrubber seems like a good fit for your application, read more about how McLanahan helped a Colombian processor with their challenges.
