US 4,375,454 AGrant
Electrostatic Enrichment of Trona and Nahcolite Ores
Issue Date:1983-03-01
•10 Claims
•3 Drawing Sheets
Abstract
Calcined trona and/or nahcolite bearing ore particles are separated into a plurality of fractions of relatively uniform particle size. Those calcined particles smaller than about 6.7 mm in size and larger than about 0.2 mm in size are passed through an electrostatic separator to obtain an ore concentrate containing a greater percentage of soda ash and a lesser percentage of insoluble impurities than were present in the ore; a middling fraction and an ore tailing fraction containing a lesser percentage of soda ash and a greater percentage of insoluble impurities than were present in the ore. The middling fraction may be recycled to increase the yield of ore concentrate. Calcined particles smaller than about 0.2 mm may be combined with the ore concentrate. The combined ore concentrate fraction may be marked as technical grade soda ash or used as a high grade feed to a monohydrate refining process.
Metadata
Assignee
- Intermountain Research and Development Corporation
Inventors
- Eugene G. Imperto
- Orval H. Hilliard
Application Information
Application Number:US 2158868
Filing Date:1980-12-12
Priority Date:1980-12-12
Art Unit:113
Classifications
IPC:
C22B 2610B03C 700B03C 100C01D 3124
Field of Search:
42323207421;206 T302 T127 A;127 R;127 C;128;129;130;131
Patent Drawings (3 sheets)
Description
This invention relates to the beneficiation of trona and nahcolite ores.
Soda ash may be produced from natural crude trona or nahcolite ore by crushing, calcining the ore at an elevated temperature to form sodium carbonate and to remove organic materials, dissolving the calcined ore in water and filtering to remove insolubles. The oil shale and other gangue minerals admixed with trona and/or nahcolite bearing ores have always been a problem as such insolubles decrease efficiency and increase the cost of operation.
One approach to the separation of oil shale from a pure grade of trona ore by selectively pulverizing the ore and screening is described in U.S. Pat. No. 3,244,476 issued to Intermountain Research and Development Corporation. This method is effective in reducing the insolubles present in material that has been repeatedly passed through rollers and pulverized to a particle size less than 0.84 mm.
This process would appear to be ineffective in the beneficiation of nahcolite bearing oil shales containing large amounts of insolubles and does not enrich calcined ore particles larger than 0.84 mm.
It is an object of the present invention to beneficiate trona and/or nahcolite ores by reducing the insoluble impurities associated therewith.
Another object of this invention is to upgrade trona and/or nahcolite ores and produce a purified feed useful in the monohydrate process for the manufacture of soda ash.
Yet another object of this invention is to produce a technical grade of soda ash by a process that is less expensive than the conventional wet process.
In accordance with the present invention, trona and/or nahcolite ore, containing sodium carbonate in combination with insoluble impurities is beneficiated by separating calcined ore particles into a plurality of fractions containing particles of relatively uniform particle size, and passing each sized fraction through a high voltage gradient thereby effecting a second separation into an ore concentrate containing a greater percentage of sodium carbonate and a lesser percentage of insoluble impurities than were present in the sized fraction, and ore tailings containing a lesser percentage of sodium carbonate and a greater percentage of insoluble impurities than were present in that sized fraction.
The ore may be crushed prior to or after calcining. The calcined ore particles are then separated into a plurality of fractions of different particle size. Those fractions having a particle size of from about 6.35 mm to about 0.2 mm are passed through a high voltage gradient, i.e., an electrostatic separator or a high tension separator which further divides the calcined particles fed to the separator into an ore concentrate fraction, a middling fraction and an ore tailings fraction. If desired, the middling fraction may be recycled through the separator to increase the yield of ore concentrate. The calcined ore particles having a size of less than about 0.2 mm may be added directly to the ore concentrate fraction.
The ore concentrate fraction that results from this process contains a greater percentage of sodium carbonate and a lesser percentage of insoluble impurities than were present in the original ore. Moreover, the ore tailings fraction from the electrostatic separator contains a lesser percentage of sodium carbonate and a greater percentage of insoluble impurities than were present in the original ore.
In carrying out the process of this invention, the trona (or nahcolite) may first be crushed to a size range which can be processed by high tension or electostatic separators, i.e., to about -6.7 mm and then calcined. Alternatively, the ore may first be calcined and then crushed as this will result in increasing the formation of smaller particles. It is necessary, however, that the ore be calcined to provide at least a surface layer of sodium carbonate on the trona (or nahcolite) particles to render them readily separable from the (calcined) gangue minerals by passing the particles through a high voltage gradient.
The crushed, calcined trona (or nahcolite) ore should preferably be separated into sized fractions so that the largest and smallest particles within a fraction are similar in mass and surface area. This is a requisite for good operating practice with high tension (or electrostatic) separation. A workable scheme would be one separating calcined ore into the following fractions: 6.7.times.1.7 mm, 1.7.times.0.5 mm, 0.5.times.0.212 mm and -0.212 mm.
It has been observed that the -0.212 mm calcined material, separated by sizing, is a concentrate product of higher soluble alkali (sodium carbonate) content than are the larger sized fractions. This fraction requires no further processing to be utilized as an upgraded feed for a monohydrate process (or other wet process) for production of refined soda ash.
The sized fractions of calcined trona (or nahcolite) ore particles may be separated electrostatically into pinned products [contains most of the gangue (shale)]; pulled or thrown products (assays very high in soluble alkali values); and middling products. The middling product may be passed through additional stages of separation (or recirculated) until it eventually leaves in either the pinned or pulled (thrown) product streams as a tailing fraction or concentrate fraction, respectively.
In the process to be described, trona and nahcolite are substantially liberated from the associated gangue minerals (such as oil shale), which cannot be separated by selective mining, by (1) size reduction to -6.7 mm, (2) calcination, (3) sizing and (4) high tension or electrostatic separation.
It is known by those skilled in the art, that after calcination, trona and nahcolite are much more readily reduced in particle size by comminution, than are the associated gangue minerals (such as oil shale). This is because the trona and nahcolite lose relatively more strength during calcination than the gangue. Attrition inherent in the calcination processes accentuates the "movement" of soluble alkali values into the fines fraction, separable by sizing.
Applicants have observed that the relative conductivity and other electrical properties of the mineral particles are altered by calcination to accentuate the difference between trona (or nahcolite) and the associated gangue (such as oil shale) so that these particles become readily separable in a high potential electrostatic field or by high tension separation.
In order to better understand the present invention and the advantages occurring from its use some alternative embodiments thereof will now be described by way of examples which are not to be considered as limiting the invention in any way.
Alternative embodiments of this invention will be better understood by reference to the attached drawings wherein:
FIG. 1 shows a generalized flow sheet of the process to be described.
FIG. 2 illustrates a Bullock-Simpson Electrostatic Separator and shows the material flow.
FIG. 3 illustrates a CARPCO Laboratory model high tension separator and shows the material flow.
Referring now to FIG. 1, the trona and/or nahcolite ore 1 may be crushed 3, and screened 5. The larger particles that do not pass through the screen (+6.35 mm) are returned to the crusher 3. Those smaller particles that pass through the screen 5 are calcined 7 at a temperature of about 400.degree. C. for 10 to 15 minutes to provide a surface coating of sodium carbonate on the trona (or nahcolite). Fuel and air, 9, are supplied to the calciner for combustion. The off gases from the calciner 7 escape through a cyclone separator 11 to a stack 13. Calciner fines 15 that are entrained in the off gases are removed in the separator 11 and collected with other soda ash concentrates in a container 31.
The calciner spill 17 is sized by passing through consecutively smaller screens. In the example illustrated, the first screen 19 has openings of 1.7 mm and calcined particles retained on this screen are passed through a high voltage gradient, i.e., high tension or electrostatic separator 25. The soda ash concentrate from separator 25 is collected in the container 31 and the insoluble ore tailings from the separator 25 is collected with other insoluble tailings in the container 33.
In the example illustrated by FIG. 1, calcined spill particles smaller than 1.7 mm and larger than 0.5 mm pass through the screen 19 and are collected on screen 21. The calcined particles retained on screen 21 are passed through a high voltage gradient, i.e., a high tension or electrostatic separator 27. The soda ash concentrate from the separator 27 is collected in the container 31 and the insoluble ore tailings from the separator 27 are collected in the container 33.
In the example illustrated by FIG. 1, calcined spill particles smaller than 0.5 mm and larger than 0.212 mm are collected on a screen 23. The calcined particles retained on the screen 23 are passed through a high voltage gradient, i.e., a high tension or electrostatic separator 29. The soda ash concentrate from the separator 29 is collected in the container 31 and the insoluble ore tailings from the separator 25 are collected with other insoluble tailings in the container 33.
In the example illustrated by FIG. 1, calcined spill particles smaller than 0.212 mm fall through the screen 23 and are added to the soda ash concentrate in container 31. The soda ash concentrate from container 31 may be used in the monohydrate process 35 to give a refined soda ash 37. Insoluble tailings from the monohydrate process 35 may be added to container 33.
In the following examples, Examples I-VI illustrate the use of electrostatic separation and Example VII illustrates the use of high tension separation.
EXAMPLE I
A sample of a nahcolite bearing oil shale containing 44.41% solubles and 55.59 insolubles is first crushed and then sized by passing through Tyler Standard Screen Scale Sieves. The size analysis and distribution of values by sized fraction is summarized in Table I. It will be noted that the smaller particle fractions contain a higher percentage of nahcolite and a lower percentage of insolubles than the nahcolite bearing oil shale (heads) prior to sizing, showing that beneficiation of an uncalcined nahcolite oil bearing shale by sizing is significant.
Portions of uncalcined sized fractions identified in Table I above are treated on the Bullock-Simpson Electrostatic Separator manufactured by the National Engineering Company of Chicago, Illinois and illustrated in FIG. 2. As shown in FIG. 2, the Bullock-Simpson Electrostatic Separator is provided with a feed hopper 36, a clockwise rotating grounded feed roll which may be constructed of brass, a counterclockwise rotating dielectric roll 38 which may be constructed of rubber, a high voltage supply 39, means for adjusting the roll to roll horizontal angle .alpha. (not shown) and splitters 40 and 41 which may separate the feed into a pulled or thrown product (concentrate fraction 42), a middling fraction 43, and a pinned or non-conductor product (tailings fraction 44). A wide range of machine parameters were tried with no apparent separation of nahcolite. The uncalcined particles were not "active" in the electrostatic field, even at 20 KV.
EXAMPLE II
The sample of nahcolite bearing oil shale described above in Example I and Table I is surface calcined by drying overnight at 110.degree. C. and is then processed on a Bullock-Simpson Electrostatic Separator at 21.degree. C. under the following conditions:
The beneficiation by sizing, and electrostatic separator of the surface calcined ore sample of Example I is shown in Table II.
It will be noted that fractions obtained by the combined steps of sizing, calcining and electrostatic separation assay as high as 82.80% solubles and as low as 17.87 insolubles.
By contrast, the nahcolite oil bearing shale of Example I contains 44.41% solubles and 55.59% insolubles.
A summary metallurgical balance of the beneficiation by sizing and electrostatic separation of this ore of Example I is given in Table III.
EXAMPLE III
A second sample of a nahcolite bearing oil shale from a different location than the ore sample described in Example I above is crushed and subjected to a size analysis by passing through Tyler Standard Screen Scale Sieve. The size and value distribution are reported in Table IV below.
Portions of the uncalcined sized fractions of this second Sample (see Example III and Table IV above) were then tested on the Bullock-Simpson Electrostatic Separator using the following operating conditions:
The particles as tested were not "active" in the electrostatic field even at 20 kilovolts.
EXAMPLE IV
The sample of nahcolite bearing oil shale described above in Example III and Table IV is surface calcined by drying overnight at 110.degree. C. and is then processed on a Bullock-Simpson Electrostatic Separator at 21.degree. C. under the following conditions:
The beneficiation by sizing and electrostatic separation of the surface calcined ore sample of Example III is shown in Table V.
A summary metallurgical balance of the beneficiation by sizing and electrostatic separation of this ore of Example III is given in Table VI.
EXAMPLE V
Uncalcined Trona Ore
Electrostatic Separation
A grab sample of trona ore which had been crushed to -8.26 mm was taken from material "in process" at a monohydrate-process plant, ahead of the calciner. A kilogram of the sample was split out for a size analysis which yielded the following data.
Fifty and one hundred gram portions of sized fractions 3, 4, 5, 6, 7 and 8 were processed with a Bullock-Simpson Electrostatic Separator. Operating parameters of the machine were varied over a wide range, as indicated in Table VII, with no effective separation occurring in any test on uncalcined trona ore.
EXAMPLE VI
Calcined Trona Ore
Electrostatic Separation
A grab sample of trona ore which had been crushed to -8.26 mm and calcined at 125.degree. C.-250.degree. C. in a rotary calciner for one-half hour was taken as "calciner spill" material at a monohydrate process soda ash plant. A kilogram of the sample was split out for size analysis which yielded the following data:
Fifty and one hundred gram portions of sized fractions split from the calciner spill sample were processed with a Bullock-Simpson Electrostatic Separator. Operating parameters were varied over a wide range (see Table VIII below), with good apparent separation of the calcined trona from gangue (shale/insoluble) particles. Selected test results are shown in Table IX.
From the test results indicated in Table IX, it may be seen that insolubles are concentrated in the tailing product and the concentrate "total alkali" assays are significantly upgraded (see calculated head assay). It is also apparent that the smaller-particle fraction (No. 8) contains less insoluble material and is not beneficiated as efficiently as are fractions 6 and 7.
EXAMPLE VII
Calcined Trona Ore, Beneficiation by Sizing and High Tension Separation
Two calciner products were sampled at a monohydrate process soda ash plant to obtain calcined (150.degree. C.-250.degree. C.) feed for testing on a CARPCO Laboratory Model High Tension Separator manufactured by the National Engineering Company of Chicago, Illinois. One calciner product was calciner spill and its size analysis is reported in Table X below, and includes distribution of values by sized fraction. The other calciner product was calciner fines (cyclone discharge) and its size analysis is reported in Table XI.
Combined fractions and products, prepared by sizing, for beneficiation tests are represented in Table XII below.
It can be seen from Table XII that segregation by sizing has effected a very significant beneficiation, the -0.212 mm calciner spill assays over 88% TA and the calciner fines (nominally -0.212 mm) assay over 91% TA. This is an important advantage as these fines are more difficult to economically process with high tension separation than are the particles larger than 0.212 mm (up to a maximum of about 6.7 mm or 9.5 mm).
Portions of the sized and combined fractions (listed in Table XII) larger than fraction 9 (0.208 mm) were processed in a CARPCO Laboratory High Tension Separator (see FIG. 3). As shown in FIG. 3, the CARPCO Laboratory Model High Tension Separator is provided with a feed hopper 45, a clockwise rotating grounded feed roll 46, a high voltage supply 47, a wire electrode 48 and a cylindrical electrode 49, and splitters 50 and 51 which may separate the feed into a pulled or thrown product (concentrate fraction 52), a middling fraction 53, and a pinned or non-conductor product (tailings fraction 54). Operating parameters for selected tests are tabulated in Table XIII.
The results of these tests are shown in the metallurgical balance of Table XIV.
A summary of this data with appropriate inclusion of the calciner fines and other -0.212 mm material, to simulate beneficiation of the total material stream, is shown in Table XV.
As can be seen, the total alkali assay of the concentrate is increased to about 90% while the insolubles decrease to 7.2%, less than half that in the unbeneficiated feed stream.
The total concentrate may be used as a high grade feed to a monohydrate refining process.
Claims
We claim:
1. A process for beneficiating an ore containing sodium carbonate values in combination with insoluble impurities said ore being selected from the group consisting of trona bearing ore and nahcolite bearing ore, to give a product containing a greater percentage of sodium carbonate and a lesser percentage of insoluble impurities than were present in said ore which comprises: crushing said ore to a particle size smaller than about 6.7 mm, returning ore particles larger than about 6.7 mm to the crusher, calcining the crushed ore particles to provide at least a surface coating of sodium carbonate, separating fines from the calciner off-gases and collecting said fines in a container; separating the calcined ore particles into a plurality of fractions containing particles of relatively uniform particle size, collecting that sized fraction having a particle size less than about 0.212 mm in a container, passing the other sized fractions through a high voltage gradient thereby effecting a separation of said other sized fractions into an ore concentrate containing a greater percentage of sodium carbonate and a lesser percentage of insoluble impurities than were present in said other sized fractions and ore tailings containing a lesser percentage of sodium carbonate and a greater percentage of insoluble impurities than were present in said other sized fractions, collecting said ore concentrate from each of said other sized fractions in a container, and combining said fines with that sized fraction having a particle size less than about 0.212 mm and said ore concentrate from each of said other sized fractions to produce a technical grade of soda ash.
2. The process of claim 1 wherein said ore is a trona bearing ore.
3. The process of claim 2 wherein said ore is a nahcolite bearing ore.
4. The process of claim 1 wherein all of said ore particles in said plurality of fractions are less than about 6.7 mm in size.
5. The process of claim 1 wherein there is obtained by passing a sized fraction through a high voltage gradient an ore concentrate containing a greater percentage of sodium carbonate and a lesser percentage of insoluble impurities, a middling fraction and an ore tailing fraction that contains a lesser percentage of sodium carbonate and a greater percentage of insoluble impurities than said ore concentrate.
6. The process of claim 5 wherein said middling fraction is recycled through the high voltage gradient.
7. The process of claim 1 wherein the largest of said plurality of fractions contains particles from about 1.7 mm to about 6.7 mm and the smallest of said plurality of fractions contains particles from about 0.212 mm to about 0.5 mm in size.
8. A process for beneficiating an ore containing sodium carbonate values in combination with insoluble impurities said ore being selected from the group consisting of trona bearing ore and nahcolite bearing ore to give a product containing a greater percentage of sodium carbonate and a lesser percentage of insoluble impurities than were present in said ore which comprises: calcining the ore to provide at least a surface coating of sodium carbonate, separating fines from the calciner off-gases and collecting said fines in a container; crushing said calcined ore to a particle size smaller than about 6.7 mm, returning ore particles larger than about 6.7 mm to the crusher, separating the calcined ore particles smaller than about 6.7 mm into a plurality of fractions containing particles of relatively uniform particle size, collecting that sized fraction having a particle size less than about 0.212 mm in a container, passing the other sized fractions through a high voltage gradient thereby effecting a separation of said other sized fractions into an ore concentrate containing a greater percentage of sodium carbonate and a lesser percentage of insoluble impurities than were present in said other sized fractions, and ore tailings containing a lesser percentage of sodium carbonate and a greater percentage of insoluble impurities than were present in said other sized fractions, collecting said ore fraction from each of said other sized fractions in a container, and combining said fines with that sized fraction having a particle size less than about 0.212 mm and said ore concentrate from each of said other sized fractions to produce technical grade of soda ash.
9. The process of claim 8 wherein said ore is a trona bearing ore.
10. The process of claim 8 wherein said ore is a nahcolite bearing ore.
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