DE3603165C1 - Process for the electrostatic separation of salt mixtures - Google Patents

Abstract

A process is described for the electrostatic separation of salt mixtures, in particular crude potassium salts, by vortexing the finely ground salt mixture using air to give a fluidised bed in which the salt mixture is brought into contact with conditioning agent and triboelectrically charged before it is introduced into the feed apparatus of an electrostatic free-fall separator and there separated into its components. It is essential for this process that the finely divided solid or liquid conditioning agent, vortexed in an air or inert gas stream of ambient temperature, is blown directly into a region of the fluidised bed in which the temperature of the salt mixture is at least 45 DEG C.

Description

The electrostatic separation of salt mixtures, in particular crude potassium salts, in their components necessary triboelectric charging of the particles such a mixture of salt is known to be particularly effective, if on the surfaces of the particles of the salt mixture chemical conditioning agents if possible are evenly distributed. However, the is even Distribution of the relatively small numbers usually used Amounts of conditioning agents in the comparative large amount of the salt mixture technically problematic and requires a lot of energy.

According to DE-PS 10 76 593, the chemical Conditioning agent in solid or liquid Form on the surface of the particles of a salt mixture be applied in that the conditioning agent and the salt mixture intensely in a mixer be mixed.

It is also known from this publication, the Conditioning agent first on carrier substances to adsorb and then mix this with the salt mixture to mix.

Since this procedure results in an even winding of the conditioning agent on the surface of the particles of the salt mixture cannot be reached the DE-PS 26 19 026 recommended, the salt mixture with the conditioning agent transferred in gaseous state to bring in contact. In this release we you. a. already pointed out the possibility the evaporated conditioning agent directly into the Heating and charging device, such as a fluid bed dryer to initiate, together with the hot fluidizing gas. With the large-scale However, testing this possibility shows that a substantial portion of the conditioning agent get lost.  

In a salt mixture pretreated in this way, that into the feeder of an electrostatic Free fall separator flows in, can only about 27 to 38% of the amount of conditioning agent originally used be found again.

For example, this is the case for an optimal separation of raw potassium salt is necessary for Conditioning at least 50 g salicylic acid per t Use raw salt. This can be done in the separator task however, only 17 g salicylic acid / t crude salt were recovered will. This amount is about the same as the amount which is for monomolecular coverage of the surface calculate the salt mixture particles leaves and for an optimal triboelectric charging the particles of the salt mixture are completely sufficient. So go during electrostatic preparation of salt mixtures considerable amounts of conditioning agents lost and stand for the intended Effect no longer available.

Therefore, possibilities were sought, the need of conditioning agents so far that he for monomolecular coverage of the surfaces the necessary amount of the salt mixture particles comes close and still an optimal triboelectric Charging followed by electrostatic separation of the components of the salt mixture can.

There has been an electrostatic separation process of salt mixtures, in particular crude potassium salts Whirl up the finely ground salt mixture using Air to a fluidized bed in which the salt mixture Conditioners contacted and triboelectric is charged before it enters the feeder  of an electrostatic free-fall separator introduced and separated into its components there will be found.

Then the finely divided solid or liquid conditioning agent in a stream of air or inert gas whirled up from ambient temperature, directly into one Area of the fluidized bed in which the temperature of the salt mixture is at least 45 ° C.

Only then will the conditioning agent be advantageous blown into the fluid bed of the salt mixture after the latter largely freed from entrained dust is.

As a rule, this condition is present if that Conditioning agent approximately in the middle of the length of the The fluidized bed is blown into the fluidized salt mixture becomes.

The conditioning agent is particularly advantageous little above the inflow floor and below the overlying heating devices in the fluid bed of the salt mixture.

It was further found that when performing there are advantages of the claimed method, when the salt mixture is blown in from below Air flows fluidized to a bed height of 30 to 120 cm becomes.

According to the method of the invention, the conditioning agent in finely divided solid form or as Liquid or solution in an air stream of ambient temperature divided without substantial quantities of the conditioning agent are in vapor form. Of course, instead of a conditioning agent also mixtures of conditioning agents can be used for the method of the invention.  

That parted in the airflow from ambient temperature Conditioning agent is according to the invention directly in an area of the fluidized bed from the particles of the Blended salt mixture, in which their temperature at least Is 45 ° C. The aim here is that the conditioning agent contained in the air or inert gas stream in the hottest zone of the fluidized bed whirled up salt mixture is blown.

This prevents premature evaporation losses, which so far has only been achieved through increased use of conditioning agents are compensated could.

There can also be unnecessary losses of conditioning agents avoid if this is only in the Fluid bed of the salt mixture is blown in after it is largely free of any dust carried along. There here the dust in a previous phase of Treatment process already from the salt batch is separated off before using conditioning agents is mixed, the separated dust is from Conditioning agents are largely free and can be unproblematic processed as part of a dissolving operation will.

As is known, when passing through a fluid bed dryer the salt mixture is first cleaned of dust and then dried by using as a fluidizing gas preheated air is used. This drying of the fluidized salt mixture is approximately in the middle the length of the fluidized bed ended, so that there Zone is in which the fluidized salt mixture highest temperature reached in the process. It has been shown that a particularly good distribution of the conditioning agent on the surfaces  the salt particle is reached when that in the air or conditioning agent divided into an inert gas stream at this point in the bed of the fluidized salt particles is blown in.

It affects the occupancy of the Salt particle surface with conditioning agents off if the air or inert gas flow with that in it distributed conditioning agent a little above the Inflow floor and below the heating devices above blown into the fluid bed of the salt mixture becomes.

It also has a beneficial effect on the distribution of the conditioning agent from when the salt mixture to a Bed height of 30 to 120 cm is fluidized.

With the method of the invention are comparable among others Conditions at a significantly reduced Conditioning agent expense the same Separation results achieved as with the previously known Method.

The measures of the method of the invention bring about also that with the released into the atmosphere Exhaust air still extremely small amounts of conditioning agents be released into the environment. There are before all according to the method of the invention except the devices, that remove dust from this exhaust air, none other technical facilities necessary to carried conditioning agent from the exhaust air isolate. When carrying out a special variant of the method according to the invention can in the salt mixture existing dust should be isolated before that Batch of salt applied with conditioning agents becomes. If this salt dust then goes to a dissolving operation is supplied, the pH value decreases the release eye is not that special setting this pH when using the method salt dust obtained according to the invention is not required is.  

If, on the other hand, one is already using conditioning agents loaded salt dust brought into a dissolving operation, the pH value of the solvent will drop to about this 2 and must then be corrected to about 5 again.

For performing the examples below is a ground crude potassium salt with 10.6 wt .-% K₂O used been the rest of the following compositions Has:

• 16.8% by weight Sylvin
  21.9% by weight of kieserite
  60.3% by weight rock salt
  1.0% by weight anhydrite

The salicylic acid used as a conditioning agent is in a finely divided, solid form in the fluidized, heated raw potassium salt blown in. The salt mixture is thus in intimate contact with the conditioning agent brought, triboelectrically charged and in one Free fall separator with a field strength of 4 kV / cm in Resource concentrate and residue separated. This in The middle goods accruing to the separator are circulated managed and thus completely worked up.  

Example 1 (state of the art according to DE-PS 26 19 026)

In a tube chute, 75 g / t salicylic acid are applied in vapor form to the crude potassium salt, which is used in an amount of 100 t / h, ie 7.5 kg / h salicylic acid are used. The following are received at the separator discharge:

The K₂O yield is 90.6%, and the loss Salicylic acid is 3.8 kg / h or 50.7%.  

Example 2 (Invention)

The ground crude potassium salt is in an amount of 100 t / h at a temperature of 19 ° C in the fluid bed dryer introduced, fluidized and heated. The solid salicylic acid is in the middle of the length of the Fluid bed above the inflow floor, but below of the heaters above it in a lot of 33 g / t (= 3.3 kg / h) into the fluidized salt mixture blown in.

The following are received at the separator discharge:

The K₂O yield is 90.9%, and the loss Salicylic acid is 1.0 kg / h or 30.3%.

Claims (5)

1. A process for the electrostatic separation of salt mixtures, in particular crude potassium salts, by whirling up the finely ground salt mixture by means of air to a fluidized bed in which the salt mixture is brought into contact with conditioning agent and charged triboelectrically before it is introduced into the feed device of an electrostatic free-fall separator and there into it Components is separated, characterized in that the finely divided solid or liquid conditioning agent is whirled up in an air or inert gas stream at ambient temperature and is blown directly into a region of the fluidized bed in which the temperature of the salt mixture is at least 45 ° C. 2. The method according to claim 1, characterized in that that the conditioning agent only then in the Fluid bed of the salt mixture is blown in after this is largely freed of entrained dust. 3. The method according to claim 1, characterized in that the conditioning agent in the middle of the Length of the fluidized bed in the fluidized salt mixture is blown in. 4. The method according to claims 1 to 3, characterized in that the conditioning agent is a little above of the inflow floor and below the one above Heating device in the fluid bed of the salt mixture is blown in. 5. The method according to claims 1 to 4, characterized in that the salt mixture to a bed height of 30 to 120 cm is fluidized.