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HDC 900 Horizontal Centrifuge

 Details of US Patent No. 5,616,245 High Gravity Separator - process technology for fine particle gravity separation



A  horizontal centrifugal concentrator,


HCD 900 uses centrifugal force to efficiently concentrate fine particles. 


With the arrival of the HDC 900, a new low cost, highly efficient fine particle gravity concentrator is now available. 


Typical capacities for a HDC 900 are:


                           Diameter of                  Feed Rate  

                              Basket          Ft3/hr       Coal                 Gold

                                mm                              ton/hr           ton/hr

                              900               700               55.0              75.0


The HDC 900 is designed to process fine particle size material.  The top size particle it can handle is 1/4" (6.25 mm), normal feed is 28 mesh (0.5 mm) x 0.


For gold or metal mining, the HDC 900 replaces table/flotation plants with one piece of equipment in less than one eighth the floor area. 


In coal the HDC 900 replaces froth flotation/water-only cyclones. 


In other applications, such as environmental clean-up or remediation the HDC 900 is used in place of much more complex circuitry.


The HDC 900 provides a high capacity gravity concentrator with a very small foot print. 


It can be used in fixed or mobile operations (see SDM Modular Plant) with feed capacities over 50 ton/hour depending on type of feed.



Presenting the new SDM High Density Centrifugal Jig  (HDC 900) and its applications to coal and mineral processing.


The HDC 900 is a new and unique machine for the high gravity processing of very small (down to micron size) particles previously difficult or impossible to separate by gravity.   The HDC 900 can solve many of the problems inherent in fine particle processing today.  It is specifically applicable to fine coal (especially for sulfur reduction) and precious metal processing.  The HDC 900 is adaptable to many different projects and properties, from new plants to reprocessing tailings and waste from old operations.



In coal and mineral processing the goal is to separate the particles into groups, those having value and those that do not.  The most efficient processing does this by using a natural difference between one particle and another.  The relative density of the particles is the easiest to use.   Gold has a density of  15+  compared to the waste material with a density of 2.3.  Coal has a density of  1.5  compared to the non-coal material with a density of 2.3. For particles whose size is large, this difference is sufficient to allow an easy low cost separating means.  When particles become small in size, other factors make this separation more difficult.


Most small particle processing is done in a moving stream of water.  This water is used to transport the material being processed and help carry the separated particles away from each other.  When processing particles 0.5 mm in size and larger and when there is a large difference in density between the particles, a water based gravity separation process is very efficient.  But, when the particles become smaller than 0.5 mm in size or the density difference between the particles is small, the speed with which the particles will move apart maybe less than the speed at which the water is flowing.  This prevents the particles from separating. The HDC 900 is the solution to this problem.


The HDC 900 solution is to increase the force on the particles by speeding up their movement.   Current available technology has increased this force by 5 to 10 times.  This is a significant improvement, but, still only works for a small range of sizes and densitys.   Many small particle applications cannot be processed economically with current technology.   Importantly, the HDC 900 can increase the force to 50 to 150 times which is much greater than any other available technology.  Thus, the HDC 900 can separate particles which were heretofore impossible to separate.


Several technologies have been introduced such as fine heavy media cyclones, column flotation, and air sparged cyclones to reach this improved level.  Fine heavy media cyclones (uses magnetite ground to very small size) have been used at a plant in Pennsylvania, USA.  Column flotation for coal (originally developed around 1900 but replaced by froth flotation) is in use at a few locations in West Virginia and Kentucky.  Air sparged cyclones (using a fragile, high cost, special gas permeable metal cylinder) are still in the developmental state.


Fine heavy media cyclones are efficient and work well, but are expensive to install and operate due to the complex nature of the media (finely ground magnetite) recovery circuit.  Conventional heavy media uses a magnetite ground to be less than .6 mm, this circuit uses magnetite ground to be less than .1 mm.  To reduce losses of the magnetite (reduce operating costs) a special multi-stage media recovery circuit is required.  This requires more capital and operating costs than a standard circuit. The circuit is also highly susceptible to fluctuations in the feed. 


Column flotation and air sparged cyclones are variations on conventional froth flotation.  As such they suffer some of the same limitations, i.e., lower efficiency than gravity separation and not all coal is foldable.  They both use chemicals and have to have very clean water.  The chemical use also restricts the amount of water that can be reused without adding other chemicals. The HDC 900 uses no toxic chemicals, no reagents, and emits no noxious gases.


The above processes are the most promising technologies, currently in general use.  All are expensive and difficult to control.   For small particle processing the ideal choice would be a low capital and operating cost gravity process that was tolerant of feed  and water fluctuations. 


Figure A below shows the processes currently in general use compared to the HDC 900.  All are limited to particles larger than 0.5 mm or rely on  toxic chemicals which are expensive and difficult to control.   In many places in the world, the use of toxic or potentially toxic chemicals for coal preparation is restricted or prohibited. For fine particle processing the ideal choice would be a low capital and operating cost gravity process that is tolerant of feed and water fluctuations.





The HDC 900 is a cross between horizontal centrifuges and jigs.  HDC 900s use the jigging principle assisted by centrifugal force to efficiently concentrate small particles.  Its use extends the range for gravity concentrating into areas currently restricted to froth flotation or chemical processing.


Processing costs are inversely related to the feed particle size.  Coarse particles are easier to process than fine particles.  Most coarse processing is done by a gravity process. Gravity processing depends on the specific gravity difference between the concentrate and the tails.  Fine sizes may require multi-stage or sophisticated circuitry. 


To date the best fine particle processing circuitry has been a physio-chemical process (e.g., flotation).  Now, with the HDC 900, this will change.  A new low cost, highly efficient fine particle gravity concentrator is now available.  Furthermore, the HDC 900  provides for a much better removal of sulfur and ash from coal than any existing technology.


For gold or metal mining a circuit similar to shown below would be used, with the screen oversize reporting back to the grinding circuit.  The material processed must be amenable to gravity processing.  But beyond that, the use of the HDC 900 will allow maximum capacity in a very small package.   Furthermore the HDC 900 provides a much better and a much greater recovery of material than any alternative technology.



In coal operations the HDC 900 would be used instead of froth flotation or water-only cyclones.  The following flow diagram shows typical coal circuit processing 1/4" x 0 feed.  In a coal operation the HDC 900 would become the fines cleaning circuit.  For deep cleaning, the HDC 900 could be a second stage following a coarse first stage.  The first stage product being crushed to 1/4" x 0.  This would produce maximum sulfur rejection at maximum combustible recovery.


The HDC 900 will be extremely efficient in ash removal.  It can process any high ash, high sulfur feed.   Such high ash feeds are culm or gob piles such as those in the eastern U.S., or low rank coals from central Europe.  These piles are uneconomical to clean with current circuitry due to fine size of the inclusions or refuse.    Now with the development of  the HDC 900 these piles become economically  and environmentally recoverable.


In the mining industry, capacity is usually expressed in ton/hour of dry feed.   Capacity is dependent on the volume of total material (solids and water) that can flow across the basket (bed) in a specific period of time.  It is also dependent on the average particle size being fed to it.  The smaller the average particle size the lower the net throughput, because the particles are closer together.  Jigs are dependent on the free settling of particles through the mobile (pulsed) bed.  Whether the unit is processing coal, gold, or some other material, the basic through put is the same on a volumetric basis.  The rated capacity in tons per hour is dependent on the specific gravity of the material being fed.


The HDC 900 can be used in fixed or mobile operations with feed capacities over 100 ton/hour depending on the type of feed. Further, it is relatively small in size for the HDC 900’s capacity to process material.   The HDC 900 has high efficiency, high recovery,  and high capacity.  The rated capacities for a HDC 900 are:



                       Diameter of                  Feed Rate  

                              Basket          Ft3/hr       Coal                 Gold

                                mm                              ton/hr           ton/hr

                              900               700               55.0              75.0


 The HDC 900 is designed to process fine particle size material.  The top size particle it can handle is 1/4" (6.25 mm). (Any larger size particles must be crushed to 1/4” or less to be processed.)


The HDC 900 is a gravity concentrating device.   With a jig, separation is into layers with the heaviest particles on the bottom and the lightest particles on the top.   The jig separates particles into two or more layers dependent upon their relative differences in specific gravity.  To make this separation, three effects (hindered settling, differential acceleration, and consolidation trickling) are the principles behind this action. 


In a jig, raw feed enters at one end, flows across the jig and out the other end.  In a standard jig, this is a flat ribbon of material constrained by the edges of the jig.  In a HDC 900, the bed is wrapped into a cylinder with the material flowing along the walls of the cylinder.  Below the feed is a deck in a flat jig and a basket in a HDC 900.  Across this deck or basket flows a bed of material.  In jigging, two effects make the separation.  The first is the opening or expansion of the bed. Secondly, the expansion is followed by the collapse or closing of the bed.  Each opening and closing is called one jig cycle.  The opening allows the particles to move away from each other, and during the closing hindered settling, differential acceleration, and consolidation trickling cause the material to separate into layers of different specific gravity.


Many methods can be used to achieve good stratification, but unless the stratified layers can be removed without remixing, all jigging advantages are lost. The problems of successful removal of the stratified layers have received a lot of attention to date.  Many of the differences between a successful jig and a poor jig depend on the design of the system to remove the different layers.


Removal of the bottom layers is usually achieved by allowing it to go through the jig bed and report to the hutch.  A key to good jigging is how the two mineral species layers are removed.  The top material reports over the weir with minimal bottom material.  And the bottom material reports to the hutch with minimal top material.


In a HDC 900, the design and operation of the refuse gate mechanism is very important.  If the gate opening is too large, too much top product will report through it.  If the gate is too small, too much bottom product will overflow the weir instead of reporting to the hutch.  As feed and operating conditions change the gate setting must be adjusted.


The HDC 900’s proprietary and patented weir mechanism used in the separation process overcomes problems associated with the cylindrical shape of the bed to provide a uniform and precise action for controlling both the flow of water and solids over the weir and the extraction of  products.



In summary:


1.  The HDC 900 is a new and unique patented coal preparation system, applicable to a wide range of coal, minerals, and soil remediation. 


2. The HDC 900 is ready for commercial production and use.


3. The HDC 900 offers a low cost alternative to expensive and potentially toxic processes for recovering fine coal.



4. The HDC 900 provides the best solution in the separation and removal of sulfur and ash from the coal, recovery of minerals, and soil remediation, all of which previously were either too difficult or impossible to economically recover. 


MIke Albrecht, P.E.

o   40+ years’ experience in the mining industry with strong mineral processing experience in precious metals, copper, industrial minerals, coal, and phosphate

o   Operational experience in precious metals, coal, and phosphate plus in petrochemicals.

o   Extensive experience performing studies and determining feasibility in the US and international (United States, Canada, Mexico, Ecuador, Columbia, Venezuela, Chile, China, India, Indonesia, and Greece).

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