Technical field
[0001] The invention relates to benefication of mineral deposits and can be used for benefication
of wollastonite ores.
Background art
[0002] A known method for benefication of wollastonite ores comprises dry crushing of the
ore in an inertial cone crusher or an autogenous grinding mill similar to "Aerofol"
and air sizing into categories of 1.0 and 0.071 mm: category +1.0 mm is sent to recrushing,
category - 0.071 mm is extracted as final wollastonite product and category- 1.0+0.071
mm is sent to magnetic separation, obtaining garnet concentrate. Prior to extraction
of wollastonite concentrate the non-magnetic product is subjected to friction electrification,
heating it to a temperature of 150-170°C in an electric tube furnace and then cooling
it down to a temperature of 100-110°C on the tray of a vibration feeder. The wollastonite
concentrate is extracted by means of electrostatic separation with simultaneous extraction
of calcite concentrate and quartz product, setting the electric field intensity in
the range of 3.5-10
5-3.9-10
5 V/m, see
RU 2002513C1.
[0003] The disadvantages of the described known method consist in its complexity caused
by the need to perform thermal treatment in strictly specific temperature conditions,
and in the low quality of the vendible product, which is obtained as two sorts of
wollastonite concentrate. The first sort of concentrate, which is obtained by air
sizing of the material of category -0.071 from crushed initial ore, has high contents
of calcite and gannet that contaminate the wollastonite product. In addition, the
method of friction electrification used for separation of the material and extraction
of the second sort of concentrate does not allow obtaining a high-quality vendible
product.
[0004] Another known method for dry benefication of wollastonite ore comprises dry crushing
of the ore, X-ray fluorescent separation of the crushed material, grinding and classification
of the beneficated material according to grain-size categories with subsequent magnetic
and electrostatic separation in order to remove the impurities and subsequent grinding
of the obtained wollastonite concentrate.
[0005] In the described known method, prior to grinding of the ore which is performed in
an inertial cone crusher or a grinding mill "Aerofol", the ore is subjected to screening
with size-grading, whereupon category +50 mm is sent to recrushing, category -10 mm
is sent to grinding and categories 20+10 mm and -50+20 mm are sent to X-ray fluorescent
separation; pieces with low content of wollastonite are removed to tailings, whereupon
the beneficated ore and grain-size category -10 mm are subjected to grinding in an
inertial cone crusher until obtaining -3 mm, which is then used to extract -0.1 mm
grain-size category by means of air sizing, thus obtaining the first wollastonite
concentrate with wollastonite content of 85%, whereas grain-size category - 3+0.1
mm is put through a magnetic separator, producing garnet-pyroxene concentrate, and
the non-magnetic product is sent to a rotary high-speed mill, using the ground material
to extract grain-size category -0.063 mm by means of air sizing, thus obtaining the
second wollastonite concentrate with at least 90% of wollastonite content, whereupon
the grain-size category -0.5+0.063 mm is subjected to magnetic separation, extracting
grains of garnet and pyroxene which are opened during further grinding, as well as
tool iron, while the non-magnetic material in the form of calcite, quartzite and wollastonite
is dried and separated in a two-stage electrostatic separator, where needle-shaped
wollastonite drifts towards the high-voltage electrode, while the admixtures, having
a rounder and slightly elongated form, push away from the high-voltage electrode and
go to the quartz-wollastonite concentrate. Elongated needle-shaped grains of wollastonite
are supplied to a disintegrator, where they are ground to grain-size category -0.040
mm, thus obtaining the third wollastonite concentrate with wollastonite content of
90%, see
RU 2142348 C1.
[0006] A serious disadvantage of the described known method consists in the low quality
of the vendible product. The described known method produces three wollastonite concentrates.
The first wollastonite concentrate WCT-1, obtained through air sizing of products
of crushing of the initial ore, cannot be regarded as a wollastonite concentrate,
since it does not pass through magnetic or electrostatic separation and contains the
entire range of impurities (garnets, calcites, pyroxenes, quartzites etc.), which
are present in the initial ore. In fact, it is the product of crushing of the initial
ore down to grain-size category of-0.1 mm.
[0007] The second wollastonite concentrate WCT-2 obtained according to the described known
method is in fact a calcite-wollastonite concentrate, since it is extracted prior
to electrostatic separation, and the contents of calcite and other non-magnetic impurities
in this concentrate are greater than or equal to the contents of these impurities
in the ore, which has a negative impact on the quality of the vendible product.
[0008] According to the described known method, air sizing is used to extract material of
grain-size category - 3+0.1 mm, which is then sent to magnetic and electrostatic separation.
The air sizing method is known to be effective for separation of particles of materials
with identical or similar density. Experiments that were conducted in the conditions
of the described known method showed that the specified material comprises mineral
particles of different density and therefore it is virtually impossible to obtain
material strictly within the specified grain-size range of- 3+0.1 mm by means of air
sizing. Usually the final contents include particles larger than 3 mm and, most importantly,
quite a lot of particles smaller than 0.1 mm. Contemporary magnetic and electrostatic
separators cannot provide high-quality purification of wollastonite (elimination of
admixtures) with such wide grain-size range (-3+0.1 mm) of the material, which also
contains high amounts of small particles (smaller than 0.1 mm).
[0009] In addition, the upper limit of the grain-size category of the material supplied
to the first stage of magnetic separation is significantly greater than the limit
of grain size of the material that provides maximum liberation of attachments of minerals.
After passing through the magnetic separator, the material that contains high amount
of particles with unliberated mineral attachments either goes to the final product
and contaminates it after regrinding, or goes to the waste, reducing the extraction
of wollastonite from the ore.
[0010] Another known method for benefication of wollastonite ore comprises primary crushing
of the ore during the first stage, directly followed by X-ray fluorescent separation,
which separates the bare (empty) rock - the tailings. Directly after the X-ray fluorescent
separation the remaining ore (without the tailings) is dried and then subjected to
secondary crushing. Then the material is divided into grain-size categories, the classification
involving only screening of the material. After the screening the material with grain-size
category of +dp is sent to regrinding, material with grain-size category of 1 < dmax/
dmin ≤ 5 is subjected to magnetic separation, first on a belt conveyor and then on
a roll-type magnetic stator. Material that has grain-size category - 0.1 dp after
the screening is extracted as the final product after air sizing. Directly after the
magnetic separation and extraction of the tool iron, garnet, pyroxene etc. the electric
separation is performed, see
RU 2292963 C1.
[0011] This engineering solution has been taken as a prototype of the present invention.
[0012] The prototype method has several disadvantages.
[0013] Since the X-ray fluorescent separation is performed directly after the primary (first)
crushing of the ore, there is significant output of wollastonite into tailings (about
20-25%). Flour particles of the material are collected only during the screening and
are not collected during preceding crushing stages, which results in loss of the wollastonite-iferous
material.
[0014] Flour particles of the material are selected as the final product (Voksil M100 and
Voksil A) immediately after the screening, without passing through the magnetic or
electrostatic separation. As a result, the product contains a lot of impurities (garnets,
calcites, pyroxenes, quartzites etc.) that are present in the initial ore.
[0015] The lack of additional drying of the material prior to electrostatic separation causes
agglomeration of particles of the material; in addition, the presence of moisture
during electrostatic separation prevents polarization of the material particles, thus
lowering the quality of separation.
[0016] It also should be noted that the prototype method does not include the step of removing
electrostatic charge from wollastonite particles, which they acquire during electrostatic
separation and grinding; this results in coupling of particles due to interaction
of opposite poles and thus lowers the product quality.
Summary of the invention
[0017] It is an object of the present invention to reduce the amount of wollastonite that
goes into waste and improve the quality of the final product.
[0018] According to the inventive method for dry benefication of wollastonite ore, which
comprises primary and secondary crushing of the ore, drying of the material, X-ray
fluorescent separation of the crushed material, classification of the material according
to grain-size categories, magnetic separation on a belt conveyor, magnetic separation
on a roll-type separator in order to remove impurities from wollastonite concentrate
of various grain sizes, grinding, as well as extraction of flour particles of the
material, the drying of the material is performed between the primary and secondary
crushing stages, the X-ray fluorescent separation is performed after the secondary
crushing, the classification according to grain-size categories is performed immediately
after the X-ray fluorescent separation by sequentially carrying out impact grinding,
magnetic separation on a belt conveyor and air sizing, followed by magnetic separation
on a roll-type separator; the extraction of flour particles of the material is performed
at the primary and secondary crushing stages and during the impact grinding of the
ore, wherein all extracted flour particles are supplied to one of the rolls of the
roll-type magnetic separator; the wollastonite concentrate of one or more grain sizes
can be dried, which is followed by electrostatic separation of the dried concentrate
in order to remove impurities therefrom, followed by air sizing of the product obtained
after electrostatic separation in order to divide it into fractions with different
grain sizes: one or more product fractions can be additionally ground, which is followed
by removal of the electrostatic charge.
[0019] The applicant has not found any sources of information containing data on engineering
solutions identical to the present invention, which enables to conclude that the invention
conforms to the criterion "Novelty" (N).
[0020] Realization of the features of the invention provides a significant decrease of wollastonite
waste, since the X-ray fluorescent separation is performed after the second (secondary)
crushing. Loss of wollastonite is also reduced due to the fact that flour particles
of the material are extracted at all crushing stages and during impact grinding, not
only during screening as in the prototype. In addition, the fact that flour particles
of the material are subjected to magnetic or, additionally, electrostatic separation
reduces the amount of impurities in the product. The quality of electrostatic separation
and, therefore, of the product is improved due to additional drying of the material
before the separation, because it reduces agglomeration of the material particles.
[0021] The applicant has not found any sources of information containing data on the influence
of the features of the invention on the technical result produced by the invention,
which enables to conclude that the invention conforms to the criterion "inventive
Step" (IS).
Brief description of the drawings
[0022] The invention is further explained, by way of example, with reference to the drawing
that shows a flow diagram of the process, in which:
- 1 -
- ore;
- 2 -
- primary crushing;
- 3 -
- drying;
- 4 -
- secondary crushing;
- 5 -
- X-ray fluorescent separation;
- 6 -
- tailings;
- 7 -
- grinding (impact);
- 8 -
- magnetic separation (belt conveyor);
- 9 -
- tool iron and strong magnetic admixtures;
- 10 -
- air sizing;
- 11 -
- magnetic separation (roll-type separator);
- 12 -
- 1st roll;
- 13 -
- 2nd roll;
- 14 -
- cyclone;
- 15 -
- garnet-pyroxene concentrate (GPC);
- 16 -
- wollastonite concentrate (WCT1);
- 17 -
- garnet-pyroxene concentrate (GPC);
- 18 -
- wollastonite concentrate (WCT1);
- 19 -
- drying;
- 20 -
- electrostatic separation;
- 21 -
- quartz-calcite concentrate (QCC);
- 22 -
- air sizing;
- 23, 24, 24 -
- wollastonite concentrate (WCT2);
- 26 -
- grinding in a disintegrator;
- 27 -
- removal of electrostatic charge;
- 28 -
- wollastonite concentrate (WCT3).
Preferred embodiment
[0023] The method is implemented in the following way.
[0024] Wollastonite ore from Kain-Suu deposit (the Kyrgyz Republic) with wollastonite content
60-71% was used as raw material. Primary (first) crushing of the ore to grain size
of 100-120 mm is performed in a jaw crusher. Then the material is dried with hot air
in a container drier. After the drying the secondary crushing of the material is performed
in a vibratory crusher to grain size of 30-40 mm. Then X-ray fluorescent separation
of the material is performed, where pieces of ore with low content of wollastonite
(less than 10%) are removed to tailings, and the beneficated ore is sent to classification
according to grain-size categories, which is started by impact grinding in a rotary
high-speed mill, followed by magnetic separation on a belt conveyor with pulley magnet,
during which tool iron and strong magnetic admixtures are separated; the remaining
material is divided into grain-size categories by means of air sizing.
[0025] Then magnetic separation on a roll-type magnetic separator is performed. In this
particular example a two-roll separator is used. Larger material is supplied to one
of the rolls, whereas smaller material is supplied to the other roll, as are the flour
particles of the material, which are extracted by means of "Cyclone" device at the
primary and secondary crushing stages and during impact grinding of the ore.
[0026] Larger weak-magnetic admixtures, namely garnet-pyroxene concentrate (GPC), as well
as wollastonite concentrate (WCT1) of higher grain size, are removed from the first
roll of the magnetic separator. Wollastonite content in WCT1 is at least 92 mass %,
the average ratio of length of wollastonite grains to their diameter (L/D) is at least
10.
[0027] GPC and WCT1 with smaller grain size are extracted from the second roll. WCT1 can
be regarded as final product, and the process according to claim 1 can be considered
to be finished. GPT, which is a by-product, can be used as an abrasive material.
[0028] WCT1 can be subjected to additional drying in a tube drying furnace, whereupon electrostatic
separation of dried wollastonite concentrate is performed, separating admixtures therefrom
- quartz-calcite concentrate (QCC), which is a by-product and can be used, in particular,
in pulp and paper industry. Wollastonite concentrate (WCT2) of various grain sizes
obtained after the electrostatic separation has wollastonite content not lower than
96% and average ratio L/D not lower than 15.
[0029] WCT2 can be additionally ground in a disintegrator, whereupon electrostatic charge
is removed from wollastonite crystals in an installation that creates horizontal electromagnetic
field. Main elements of the installation are electrodes in the form of plates with
supplied DC voltage of 25 kV.
Industrial applicability
[0030] The invention can be implemented by means of common factory equipment. In applicant's
opinion, this enables to conclude that the inventions conform to the criterion "Industrial
Applicability" (IA).
1. A method for dry benefication of wollastonite ore, which comprises primary and secondary
crushing of the ore, drying of the material, X-ray fluorescent separation of the crushed
material, classification of the material according to grain-size categories, magnetic
separation on a belt conveyor, magnetic separation on a roll-type separator in order
to remove impurities from wollastonite concentrate of various grain sizes, grinding,
as well as extraction of flour particles of the material, characterized in that the drying of the material is performed between the primary and secondary crushing
stages, the X-ray fluorescent separation is performed after the secondary crushing,
the classification according to grain-size categories is performed immediately after
the X-ray fluorescent separation by sequentially carrying out impact grinding, magnetic
separation on a belt conveyor and air sizing, followed by magnetic separation on a
roll-type separator, and the extraction of flour particles of the material is performed
at the primary and secondary crushing stages and during the impact grinding of the
ore, wherein all extracted flour particles are supplied to one of the rolls of the
roll-type magnetic separator.
2. A method as claimed in claim 1,characterized in that the wollastonite concentrate of one or more grain sizes is dried, followed by electrostatic
separation of the dried concentrate in order to remove impurities therefrom, followed
by air sizing of the product obtained after electrostatic separation in order to divide
it into fractions with different grain sizes.
3. A method as claimed in claim 2, characterized in that one or more product fractions are additionally ground and the electrostatic charge
is removed.