WO1999060175A1

WO1999060175A1 - Conglomeration of minerals from a granular state with binder including waterglass, acrylic resin and vinyl alcohol

Info

Publication number: WO1999060175A1
Application number: PCT/ZA1999/000034
Authority: WO
Inventors: John Rutherford Moody
Original assignee: Mineral Enhancement South Africa (Proprietary) Limited
Priority date: 1998-05-18
Filing date: 1999-05-17
Publication date: 1999-11-25
Also published as: PL344292A1; CA2332797A1; NO20005789D0; NO20005789L; JP2002515546A; BR9910561A; TR200003388T2; AU4103199A; EP1080237A1

Abstract

The invention concerns agglomerating or briquetting of a mineral in fine granular state of less than 5 mm for smelting which may be mixed with fines by conglomerating the mineral with a binder prepared from at least sodium silicate, acrylic resin, vinyl alcohol, borax, magnesium chloride and if required during smelting an anti-oxidant such as sodium. The bound conglomerates or briquettes have superior strength properties.

Description

CONGLOMERATION OF MINERALS FROM A GRANULAR STATE WITH BINDER INCLUDING WATERGLASS, ACRYLIC RESIN AND VINYL ALCOHOL

FIELD OF THE INVENTION

This invention relates to the conglomeration of minerals, excluding carbonaceous minerals, from a granular state and more particularly but not exclusively from granules of less than 5.0 mm granule size mixed with fines.

BACKGROUND TO THE INVENTION

Many minerals are recovered from ore in a state which makes them difficult to handle, transport and use in further processing. Of particular interest in this regard may be mentioned chrome ore where many mines have large dumps of this material in fine granular form.

OBJECT OF THE INVENTION

It is the object of the present invention to provide a method of conglomerating minerals in this state and the binder for use in this method.

The term "minerals" in this specification is to be understood as excluding carbonaceous material.

SUMMARY OF THE INVENTION According to this invention there is provided a method of conglomerating a mineral in a granular state for smelting comprising admixing with the mineral an amount of 0.1% to 5% by mass of a binder including at least sodium silicate, acrylic resin, vinyl alcohol, an effective amount of a boron accelerator, a magnesium salt and an anti-oxidant where necessary for smelting and consolidating the mixture into discreet units suitable for transport and handling. The boron accelerator may be borax and the magnesium salt may be magnesium chloride.

Further features of this invention provide for appropriate compounds present in o the mineral to be conglomerated to be effective constituents in the determination of a binder for a specific mineral for the accelerator to be a boron compound and for the pH of the binder to be maintained at a pH of between 6.5 and 8.5.

Still further features of this invention provide for the conglomeration to be effected on a mineral having a particle size of less than 1.5 mm or a mixture of particle 5 sizes in the range of 1.5 mm to 5.0 mm and fines, for the binder to be used at least in part in liquid form, for the accelerator to be used in dry or low viscosity liquid form and for remaining constituents to be used in high viscosity liquid form.

The invention also provides for the mixing to be effected at ambient or elevated temperature using a ribbon or other suitable blender and for the conglomeration o to take place at elevated temperature and to be effected through heated moulds.

Still further features of this invention provide for the discreet units to be blocks or briquettes and for the units to have a size suitable for easy handling and transportation preferably having a weight of between 50 g and 1 kg.

The binder will preferably comprise constituents in the ratio

5 Sodium silicate 1% to 30%

Acrylic resin 1 % to 30%

Vinyl alcohol 1% to 20%

Borax 0.1% to 15%

Magnesium chloride 0.1 % to 10% Sodium nitrite 0.1 % to 10% by mass and have a pH of 6.5 to 8.5. The invention also provides for the conglomeration to be effected under pressure of approximately 14 000 KPA with a moisture content of less than 6% by weight in a briquetting machine.

Yet further features of this invention provide for the accelerator to be controlled by means of a buffer which is weak acidic or alkali.

Preferred embodiments of the invention are described by way of examples below.

In a first example of this invention chrome granules of an average particle size of 1.55 mm (10 microns - 2 mm) were mixed in a ribbon blender at room temperature for 3 minutes with a binder consisting of

Sodium silicate 10%

Acrylic resin 4%

Vinyl alcohol 10%

Borax 1 %

Magnesium chloride 3% Sodium nitrite 1%

The constituents were mixed in water and in the percentages given by mass.

Samples were conglomerated using a Komarek briquetting press under a pressure of approximately 14000 KPA.

The briquettes are exceptionally hard and on compression testing were found to have a compression strength of 27.0 KPA.

In a second example manganese granules of a similar size to those of the chrome in the first example given above were similarly mixed with the same binder.

The mixture was conglomerated in the same manner as the chrome and the resulting briquettes were found to have a compressive strength of 48.3 KPA.

In both examples the moisture content of the briquettes was kept below 4% by mass. The briquettes maintained their integrity at a temperature in excess of 1500°C.

Trials on a practical scale were conducted in a 100 ton mineral briquetting trial. The mineral was obtained from the Meyerton area of Gauteng, South Africa and had a particle size range of 10 microns to 2 mm.

The equipment used was that specified above.

The binder consisted of

Sodium silicate 10% as a 20% solution Acrylic resin 4% as a 46% solution Vinyl alcohol 10% as a 10% solution Borax 0.8% Magnesium chloride 2.5%

and was used as a mixture of 6% by weight with water to give an overall water content of 4.5%. The accelerator was added as dry powder

The material was briquetted in batches of 1.4 tons of silica manganese mixed with 1000 grams of dry borax accelerator with the remainder of the binder being a thick slurry. The mixing time in the ribbon blender was five minutes and the pressure in the briquetting machine was 23 Mpa.

Representative results were as follows -

Result Green Cured abrasion indices Cured crushing Weathered strength (%) strength crushing

(Number Spec > 75% Spec < 10% strength of drops (pellets survived) still wet)

Tumbler 1 Tumbler 2 MDa kα/bπq kα/bπq

Good briquettes 1.6 60.2 24.3 1.549 62.7 36.4

Good briquettes 2.0 - 1.373 55.7 -

Good briquettes 2.8 - 1.912 77.37 -

Good briquettes 3.2 56.5 28.9 1.453 58.8 42.1 Similar results obtained using a ferromanganese ore and the same binder were-

Result Green Cured abrasion indices Cured crushing Weathered strength (%) strength crushing (Number Spec > 75% Spec < 10% strength of drops (pellets survived) still wet)

Tumbler 1 Tumbler 2 Mpa kα/bπq kα/bπq

Good briquettes * ~ 2 123 85.9 - Good briquettes 3.8 10.3 48 7 1.639 66.3 33.3

Good briquettes 3.2 - 1.800 71.3 - Good briquettes 3.0 " 1.800 71.3 - Good briquettes 2.6 - 1.137 46 - Good briquettes 1.8 8 40.2 1.197 48.4 20.6

The briquettes were introduced into a furnace process wherein the furnace was not shrouded against ambient atmosphere. No violent reaction took place and the results of the alloying process were satisfactory.

The binder did not affect the properties of the minerals and affords some advantage to the smelting process. No anti-oxidant was required in the binder because the smelting furnace contents were shielded against oxidation.

It will be appreciated that the composition of the binder can be varied to obtain the best results with each mineral to be agglomerated. The most suitable recipe can be determined with reasonable experimentation and a comprehensive analysis of the minerals.

The constituents of the binder do not only conglomerate the mineral, they are selected also to have only desirable effects on the final alloy. The organic components are chosen for insolubility in the metal and become constituents in the furnace slag The organic constituents will also be chosen from food quality products to avoid contamination in that no toxic reaction products result from the use of the binder.

The inclusion of sodium silicate gives the final briquette the required resistance to temperature. It also, along with the magnesium chloride gives the product insolubility in water and thus good weathering characteristics.

The polyvinyl alcohol and acrylic resin combination gives hardness and insolubility to the final product enabling it to melt inwardly in use and the small quantities of binder required make it easy to prepare and handle. The basic binding appear to be that between mineral and polyvinyl alcohol. It is necessary that the latter be dissolved in the water during mixing and good stirring is required. Sometimes elevated temperature of the water will materially assist in reducing the mixing time required.

The binder lends itself to a wide range of constituent composition for achieving conglomeration in the most economic manner with respect both to time and composition of the binder.

The sodium nitrite constituent acts to prevent oxidation and thus dilution of constituents such as manganese as alloying elements in the final metallurgical product. Where this product is produced in an argon shrouded furnace this constituent may be omitted from the binder.

It will further be understood that if particular circumstance relating to the mineral to be conglomerated so dictate the water content of the mixture prior to introduction into the consolidating moulds may be more or less than the 6 percent referred to. Of course all water of crystalisation in the binder constituents will form part of overall moisture content under consideration. This will determine to some extent how the binder is mixed. The accelerator may be used dry or as a low viscosity slurry. This enables control over the accelerator to be maintained at a high level.

Always optimum mixing conditions will be determined by the mineral to be conglomerated and the use to which it is to be put. The best binder composition can be determined especially based on a detailed knowledge of the mineral composition. Those skilled in the art will appreciate that the binder constituents are largely determined by the final water content that can be tolerated in the conglomerated unit. This content is also effected by the costs aspects of the briquette composition where the costs of removing moisture from the mineral must be weighed against the difficulty of using binder constituents with minimum water content.

In particular the degree of saponification of the vinyl alcohol to a large extent affects the difficulty in dissolution and temperature and times needed for this process. Thus the pH control can also become important to prevent the reaction of binder constituents from taking place too rapidly when the binder is mixed into the mineral. Here the use of a buffer preferably citric acid or potassium hydroxide, chosen for a binder of a specific mineral, will also assist in the control of the binder reaction.

Further the physical characteristic of the mineral is important. Larger sized particles can be accommodated provided there is an adequate quantity of fines between the larger particles. Mixtures of this kind will require the use of less binder material and the optimum dosage rate will be proportional to the distribution of particle sizes in the mineral.

A very suitable proportionality of particle size is 1.5 mm to 2 mm - 20% by weight; -8 mm to 1 mm - 30% by weight with the remainder as powder.

As mentioned above the sodium nitrite may be omitted when the briquettes are used in a shrouded furnace. However this constituent, or an equivalent, may beneficially be included in the binder as a preservative where there is a possibility of the briquettes or blocks being stored for lengthy periods of time.

It will also be understood that the mineral may be bound into blocks rather than briquettes. This will enable mineral having larger size particles than those referred to above and a wider size range to be accommodated with the binder of this invention. Equipment suitable for this purpose is commercially available.

Claims

CLAIMS:

1. A method of conglomerating a mineral in a granular state for smelting characterised in that the minerals are admixed with an amount of 0.1% to 5% by mass of a binder including at least sodium silicate, acrylic resin, vinyl alcohol, an effective amount of boron containing compound as an accelerator, magnesium salt and an anti-oxidant where necessary for smelting, and conglomerating the mixture.

2. A process as claimed in claim 1 characterised in that the mineral has a particle size of less than 5 mm and contains fines.

3. A process as claimed in claim 2 characterised in that the mineral is in the form of a mixture of particle sizes ranging from 1.5mm to 2 mm and contains fines.

4. A process as claimed in any one of the preceding claims characterised in that appropriate compounds present in the mineral are effective constituents in the determination of a mineral specific binder.

5. A process as claimed in any one of the preceding claims characterised in that the pH of the binder is maintained between 6.5 and 8.5.

6. A process as claimed in any one of the preceding claims characterised in that the accelerator is controlled by the addition of a buffer which is weak acid or alkali.

7. A process as claimed in any one of the preceding claims characterised in that at least the resin and alcohol are mixed in water in a quantity dependant on the water content permissable in the finally conglomerated mineral.

8. A process as claimed in claim 7 characterised in that the water is added at an elevated temperature.

9. A process as claimed in any one of the preceding claims characterised in that conglomeration is effected under pressure of at least 12 000 KPA.

10. A process as claimed in any one of the preceding claims characterised in that the moisture content of the mixture fed for conglomeration is less than 6% by weight.

11. A process as claimed in any one of the preceding claims characterised in that the conglomeration is effected at elevated temperature.

12. A process as claimed in claim 11 characterised in that the conglomeration is effected in heated moulds.

13. A process as claimed in any one of the preceding claims characterised in that the binder comprises constituents in the ratio

Sodium silicate 1% to 30%

Acrylic resin 1% to 30%

Vinyl alcohol 1% to 20%

Borax 0.1% to 15%

Magnesium chloride 0.1% to 10% Sodium nitrite 0.1% to 10% by mass.

14. A process as claimed in claim 13 characterised in that the binder consists of constituents in the ratio Sodium silicate 8% - 12% Acrylic resin 2% - 5% Vinyl alcohol 8% - 12% Borax .6% - 1.1%

Magnesium chloride 2.5% - 3.1% Sodium nitrite .8% - 1.2% by mass.

15. A process as claimed in any one of the preceding claims characterised in that this mixture is consolidated into discreet units suitable for handling and transport.

16. A process as claimed in claim 15 characterised in that the mixture is consolidated into briquettes or blocks.

17. A binder for a process as claimed in any one of the preceding claims characterised in that it includes the constituents as defined in claims 1 , 3, 13 or 14.