serves to reduce the yield stress of the mud. The second pump is employed to move the lower yield stress mud from the thickener and transport it towards the placement area. Rheomalaxic muds can make dealing with the paste less expensive as centrifugal pumps may be employed and placement can make better use of the area available for the material to flow. Additionally, if the placement of the low water content mud is made in shallow“ lifts”, drying time for the mud can be greatly reduced.
So, why would someone want to go through the trouble of creating these higher yield stress muds? First, higher recovery of water and usefulness in mine backfill, as well as
being extremely beneficial to producers is the stability of the mud once in place. Higher yield stress muds pose lower risk of impoundment failure.
Success of your thickening system requires that a sound effort is made to understand the tailings. This is done by a number of suppliers through detailed settling and viscosity analysis of the muds. Methods for continuous settling tests have been developed in the past 15 years and have been shown to give a much better set of data for sizing and selection of the thickeners than static tests. Always be sure your thickener manufacturer tests your samples and material to help select the right thickener for your application.
Both the High Rate and High Density Thickeners are generally supplied with rake lifting mechanisms to pull the rakes up out the mud should a high torque condition occur. The torque is constantly monitored and as it decreases due to higher pump out rates or reduced inflow of mud, the rakes are indexed back down to their lowest position.
Paste Thickeners Paste Thickeners offer the operator the ability to produce the highest underflow concentrations and yield stress muds possible with gravity settling alone. These tanks typically have aspect ratios( height: diameter) of 1:1 to 1.5:1 and steep underflow cones ranging from 25 to 60 degrees. The principal design consideration for a Paste Thickener is the mud residence time. Paste is a term used to describe a mud from which there is little to no further segregation of free water from the solids. To further enhance the formation of the paste, rakes are often equipped with vertical rods, or angles, that protrude upward in the tank. These“ pickets” cut channels through the mud, creating passage ways for trapped water to be liberated from the mud as it compacts.
Due to the high yield stress of the muds, Paste Thickeners must often be equipped with special pumping arrangements for mud removal and transport. Positive displacement pumps such as piston or piston diaphragm pumps are often used. However, many mineral based muds will exhibit a viscosity characteristic known as rheomalaxis, which is the irreversible thinning of slurry with time as it is subjected to shear. In such cases, the underflow cone of a Paste Thickener may consist of two process pumps. One pump has the duty of withdrawing sludges and pumping it back into the cone via a“ shear loop”, which
Traffic diversion & stop signs were completely ignored by flood waters
When nearly 300mm of rain fell in 3 days, this South African mine was inundated by surface water run-off. Capital repairs and loss of earnings resulting from the 4 month closure cost over US $ 100 million.
Our diversion solution will make sure the next flood behaves the way it’ s supposed to.
If only we’ d been involved earlier we could have put that flood water in its place.
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MARCH 2018 Supplement | International Mining P9