Solution mining

1
Solution mining

• Introduction
• Technology of solution mining
• Technology of the salt production
• Geological conditions
• Pros and cons

2
Solution mining - Introduction

• The method of solution mining is a very old
  technological process. Natural brine sources
  were already used in antiquity.
• Brine was produced by squirting water into mining
  chambers as well as by injection of water in the
  deposit through wells.
• In the 50th and 60th new fields of the
  technology were developed. The present status of
  equipment of the well was developed.

• The erected cavern by solution mining often used
  as underground 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.

3
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.

4
Technology of Solution Mining (2)

• The dissolution of the salt begins with the
  solution of a cavern sump. The sump shall be
  accommodate the insolubles of the deposit near
  the casings in 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 the cavern has the same
  direction as in the production casing.
• The solution of the sump can be ended if the
  diameter of the cavern is 5 10 m.

5
Technology of Solution Mining (3)

• The next step is the undercut phase. The
  injected water is going trough 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.

6
Technology of Solution Mining (4)

• For winning of the salt in the deposit the level
  of the casings and the blanket was arranged
  higher. Because in the cavern the density of the
  brine increases from the top to the bottom, the
  brine current goes from the end of the outer
  casing under the blanket level to the side and
  then it flows to the inner casing and to the
  surface.

7
Technology of Solution Mining (5)

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

8
Technology of Solution Mining (6)

• Last of all the tubes were removed and the bore
  hole will be cemented.

9
Technology of Solution Mining (7)

• 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 and a storage, (3) a building for
  pumps, (4) a blanket station, (5-7) tanks for
  water and brine

10
Technology of Solution Mining (8)

• Another technology is used for the erection of
  underground storages. In this case the salt was
  dissolved after the undercut in only one step.
  The entry of the solvent into the cavern is
  trough the inner tube. From there the 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 cases not saturated.

11
Technology of Solution Mining (9)

• Methods to control the size of the caverns
• 1. Measurement of radial distance between the
  well and the cavern surface with ultrasonic
  sondes (sonar).
• 2. Measurement of the area by addition of
  blanket into the cavern and determination of
  height difference of the blanket level.
• 3. Mass- and volume balance of solvent injection
  and brine recovery
• This three methods used together allows an
  precise assessment of the cavern area and size.

12
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.

13
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 NaCl brine 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.
14
Technology of the salt production (3) Rock salt
Flowsheet of NaCl production in a solar pond
process
Brine
Solar pond
Harvested crystalline crop
Crushing, screening
Water
Soiled brine
Washing
Oil or gas
Water
Drying
Storage
NaCl
15
Technology of the salt production (4) Rock salt
Flowsheet of NaCl production in a technical
process
Brine
Chemical purification, precipitation of Mg,
Ca,SO4--
Steam or electrical power
Water
Evaporation, crystallisation
Water
Oil or gas
Drying
Storage
NaCl
16
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.
17
Technology of the salt production (6) Sylvinite
Flowsheet of NaCl KCl production in a technical
process
Brine
Chemical purification, precipitation of Mg,
Ca,SO4--
Steam or electrical power
Water
Evaporation, NaCl crystallisation
NaCl
Water
Soiled brine
Washing
Vaccum cooling, KCl crystallisation
Oil or gas
Water
Drying
Oil or gas
Drying
Storage
Storage
NaCl
KCl
18
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.
Carnallite crystallisation by vacuum cooling
Evaporation
Cold leaching
KCl loss by decomposition
Cold leaching
19
Technology of the salt production (8) Carnallite
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.
20
Technology of the salt production (9) Carnallite
Solution mining of carnallitite with - two
wells - selective dissolution - hot leaching
21
Technology of the salt production (10) Carnallite
22
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.
23
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.