Two-stage electrostatic separation of particulate material

Claim 2

A process as defined in claim 1, wherein said raw salts are haRtsalz.

Claim 3

A process as defined in claim 1, wherein the step of brushing said dust separately off said positive electrode comprises subjecting said positive electrode to a brushing with a stationary brush.

Claim 4

A process as defined in claim 1; and further comprising the steps of separately subjecting said additional preconcentrate to further separation into portions of higher and lower K2O concentration until a portion is obtained having a K2O concentration of between about 58 and 60 percent.

Claim 5

A process as defined in claim 1, wherein the steps of establishing said electrostatic fields comprise establishing at least said first electrostatic field at a field strength of between substantially 4.0 and 4.5 kv./cm.

Claim 6

A process as defined in claim 6, wherein the steps of establishing said electrostatic fields comprise establishing said second electrostatic field also at a field strength of between substantially 4.0 and 4.5 kv./cm.

Claim 7

A process for the continuous electrostatic separation, by means of continuous electrode surfaces of an endless, conductive, moving belt, of ground potassium raw salts containing finely divided particles and being conditioned with a 10-15 percent aqueous solution of sodium salts of straight chain, lower fatty acids, comprising the steps of establishing between two electrodes of opposite polarity in an electrostatic separator an electrostatic field having a strength of at least 3.5 and at most 4.5 kv./cm.; feeding in a predetermined direction through said electrostatic field a stream of said potassium raw salts including particles having a grain size smaller than 0.15 mm. and particles having a grain size larger than 0.15 mm. and containing a predetermined percentage range of K2O, whereby a dust concentrate consisting of particles having a grain size up to about 0.15 mm. and containing between substantially 38-42 percent K2O adheres to the positive one of said electrodes, while a dust-free potassium oxide-rich preconcentrate having a grain size greater than 0.15 mm. and containing 40-46 percent K2O flows freely toward and past said positive electrode, and a potassium-poor residue flows to the negative one of said electrodes with a middling fraction passing intermediate both of said electrodes; brushing said dust concentrate off and recovering it from said positive electrode; and returning said middling fraction upstream of said electrostatic field for renewed passage therethrough with fresh raw salts.

Claim 8

A process as defined in claim 8, wherein the step of establishing said electrostatic field comprises establishing said field at a field strength of between substantially 4.0 and 4.5 kv./cm.

Claim 9

A process as defined in claim 9, wherein said stream is passed through said field in downward direction.

Claim 10

A process as defined in claim 9, wherein said raw salts are hartsalz.

Claim 11

A process as defined in claim 9; and further comprising the step of subjecting said preconcentrate to further electrostatic separation into portions of higher and lower K2O concentration until a portion is obtained having a K2O concentration of between about 58 and 60 percent.