Solution Mining 03

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Solutionmining

Introduction

Technology of solution

mining

Technology of the salt

production

Geological conditions

Pros and cons


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Solution mining -

Introduction

The method of solution mining

is a very old technologicalprocess. Natural brine

sources were already used in

antiquity.

Brine was produced by

squirting water into mining

chambers as well as byinjection of water in the

deposit through wells.

In the 50th and 60th new fields

of the technology were

developed. The present statusof equipment of the well was

developed.

The erected cavern by

solution mining often used asunderground storages for gas

or oil.

Besides the exploitation of

rock salt other minerals

obtains a great importance

(i.e. sylvinite, carnallite,bischofite, trona).

The control and measurement

methods for steering the size

and the form of the cavities

were elaborated.


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Technology of Solution Mining (1)

A bore hole was drilled from the surface of the earth to the

bottom of the salt layer.

- A casing was worked in the bore well and was cemented from

the surface to the top side of the deposit. The cement must

shut tight against the pressure of the blanket.

- The surface of the bore hole in the area of the deposit is free.The salt can be dissolved.


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The dissolution of the salt begins with the solution of a cavern sump. Thesump shall be accommodate the insolubles of the deposit near the casingsin the well.

- During the solution of the sump only water is used .

- The water current is directly, that means that the current of brine in thecavern has the same direction as in the production casing.

- The solution of the sump can be ended if the diameter of the cavern is 510 m.


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The next step is the undercut phase. The injected water is goingtrough the outer casing and the brine leave the cavern trough the

inner casing. This current direction is named indirectly.

Important for the forming of the cavern is the precise controlling of

the blanket level.


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For winning of the salt in the deposit the level of the casings andthe blanket was arranged higher. Because in the cavern the

density of the brine increases from the top to the bottom, the brinecurrent goes from the end of the outer casing under the blanketlevel to the side and then it flows to the inner casing and to thesurface.


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The last step is reached, if the cavern arrives the top of thedeposit.


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Last of all the tubes were removed and the bore hole will becemented.


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The equipment of the brine place is very simply. For the production

of brine is needed:(1) a building for a control room and an office, (2) a workshop anda storage, (3) a building for pumps, (4) a blanket station, (5-7)tanks for water and brine


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Another technology is used for the erection of underground storages. Inthis case the salt was dissolved after the undercut in only one step. Theentry of the solvent into the cavern is trough the inner tube. From therethe solvent rises up, dissolves the salt and goes to the outer casing.

The sides of this cavern are more straightly as the caverns which is

leached with the step-by-step technology.A disadvantage of this procedure is that the brine is in the most casesnot saturated.


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Methods to control the size of the caverns

1. Measurement of radial distance between the well and thecavern surface with ultrasonic sondes (sonar).

2. Measurement of the area by addition of blanket into thecavern and determination of height difference of the blanket

level.

3. Mass- and volume balance of solvent injection and brinerecovery

This three methods used together allows anprecise assessment of the cavern area and size.


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Technology of the salt production (1)

The most important salt minerals, which

produced by solution mining are:

- Rock salt (NaCl)

- Sylvinite (NaCl + KCl)

- Carnallite (MgCl2 * KCl * 6H2O)

Because these minerals have very different thermodynamic

properties, the production technology for each salt had to

developed specifically.

How we have to see later for the winning of carnallite the

development of a new solution mining technology was

necessary.


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Technology of the salt production (2)Rock salt

The most important property of NaCl is the

independence of the saturation concentration

from the temperature.

Because of this the whole water contains in the

brine must be evaporated.

For example contains 1000 l saturated NaClbrine 317 kg KCl and 882 kg H2O.

That means the production of NaCl is a very

energetic intensive process.

In locations with arid climate often used the

evaporation in solar ponds.

Otherwise the evaporation must take place in

technical plants. As energy base is used steam

or electrical power.


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Flowsheet of NaCl production in a solar pond process

Solar pond

Brine

Crushing, screening

Harvestedcrystalline

crop

Drying

Storage

Oil or gas Water

NaCl

WashingWater Soiledbrine


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Flowsheet of NaCl production in a technical process

Chemical purification,

precipitation of Mg++, Ca++,SO4-

-

Brine

Evaporation,

crystallisation

Drying

Storage

Oil or gas

Water

NaCl

Steam or electrical

power

Water


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Technology of the salt production (5)Sylvinite

Sylvinite is a mixture of NaCl and KCl.

In the case of contact with water by solution mining will be dissolved both components. At

first in relation of their concentration in the raw salt and later the dissolution is appraoching

to the invariant point M (red line), as shown in the following picture.

10C 90C50C

Brine

NaCl - crystallisation

Evaporation

KCl - crystallisation

by coolingMixing with ML

Solution mining

0

50

100

150

200

250

300

350

400

0 50 100 150 200 250 300 350 400 450 500 550 600

KCl g/kg H2O

NaClg/kgH2O


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Technology of the salt production (6)Sylvinite

Flowsheet of NaCl + KCl production in a technical process

Chemical purification,

precipitation of Mg++, Ca++,SO4-

-

Brine

Evaporation,

NaCl crystallisation

Drying

Storage

Oil or gas

Water

KCl

Steam or

electrical power NaCl

Drying

Storage

Oil or gas Water

NaCl

Washing

Vaccum cooling,

KCl crystallisation

Water Soiledbrine


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Technology of the salt production (7)Carnallite

Carnallite is a double salt of MgCl2, KCl and six crystall water (MgCl2 * KCl * 6 H2O).

The solubility of the system Mg K Cl H2O is shown in the following diagram.

MgSO4=0 g/kg H2O

20C

0

100

200

300

400

500

0 50 100 150 200 250

KCl g/kg H2O

MgCl2g/kgH2O

80C

KCl loss by decomposition


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How we can see the cold leaching has no efficiency, because

- the brine is not high concentrated and many water

must evaporated

- the losses of KCl by decomposition of carnallite

are very high

Therefore the hot leaching technology for solution mining of

carnallite must used. This procedure has not the named

disadvantages and has the following advantages:

- The brine is high concentrated. Carnallite can be

crystallised by evaporation of a few amount of

water and cooling the brine

- The solvent is saturated on NaCl. Therefore halite

and also kieserite remain in the cavern as residue.

- In the cavern remains a high concentrated brine,

which not worries the environment.

Because the solvent has a high temperature, the cavern has

two wells as shown in the following picture. In only one well

would exchange the heat between the concentric inner and

outher tube or casing.


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Solution mining of carnallitite with:

- two wells

- selective dissolution

- hot leaching


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brine

life steam condensate

hot saturated brine

condensate

slurry

mother liquor 1:

solvent for solution mining

or prodoction of bischofite

or discharge liquor

carnallite, halite

water decomposition liquor

sylvite, halite

hot mother liquor 2 halite, wet

hot brine, KCl saturated

water condensate

slurry

mother liquor

KCl

Flow sheet for the production of KCl from carnallite brine

evaporator

evaporator, vacuum cooling,

carnallite crystallisation

vacuum cooling, KCl cristallisation

vacuum cooling, KCl cristallisation

thickener

decomposition

hot leaching


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Geological conditions

The very best to use the solution mining technology is:

- a great height of the deposit

- and a low depth

But by using new developed technologies the winning of

mineral salts in deposits with low height is possible. This new

technology is named solution mining with tunnel caverns. In

this case one bore hole was drilled verticaly and the other was

drilled at first verticaly and then it follows in the deposit the

direction of the salt layer with a deviation.

This technologie is not usable if the deposit has tectonical

breakdown and other disturbances or great changes in the

direction.

The drilling of the bore holes can be complicated and

expensivly if the overburden contains gas or water.


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Pros and cons

Pros:

- In the most cases solution mining has a very high

economic efficiency because:

- The investment costs are low. (We dont need a mine)

- The drilling of the bore holes are running costs

- The demand of manpower is low

- Solution mining can also used by difficult hydrogeological

conditions.

- The first step of the potash mill (hot leaching) is in the

underground. There are no costs for this equipment.

- Residue and high concentrated brine stays in the cavern,

therefore there environmental burdens are low.

Cons:

- If the geological and tectonical conditions are very difficult,the solution mining is not usable.

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