PVOH BINDER COMPOSITIONS AND METHODS FOR POWDERED MINERALS

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 63/675,011 filed on Jul. 24, 2024, the entire contents of which are hereby incorporated by reference.

BACKGROUND

The present disclosure relates in general to management and re-use of industrial waste by-products, and more particularly, to transportation and re-use of powdered minerals through improved binding formulations.

All of the subject matter discussed in the Background section is not necessarily prior art and should not be assumed to be prior art merely as a result of its discussion in the Background section. Along these lines, any recognition of problems in the prior art discussed in the Background section or associated with such subject matter should not be treated as prior art unless expressly stated to be prior art. Instead, the discussion of any subject matter in the Background section should be treated as part of the inventor's approach to the particular problem, which in and of itself may also be inventive.

In various industrial sectors such as mining, manufacturing, and power generation, substantial volumes of powdered minerals are generated as by-products. Powdered minerals, including but not limited to mining dust, manufacturing slags, and power plant ash/slags, are abundant globally. These fine particles, though sometimes considered waste, actually contain useful elements and compounds that can be repurposed for economic and environmental benefits. Extracting value from these by-products requires effective processing techniques.

The primary challenge lies in achieving a stable form of these powdered minerals suitable for transportation and re-use. Not only must they withstand the journey to their intended use site, including exposure to elements such as high humidity, rain, varying temperatures, and rough handling, but they must also remain stable within the expansive processing facilities at their destination. Unstable materials can lead to product loss, safety hazards, and operational inefficiencies.

To address these challenges, various stabilization methods have been explored. One promising approach involves the use of binders to transform the powdered material into briquettes. These briquettes offer several advantages, including 1) reducing the risk of explosions during handling and transportation by preventing dust dispersion and minimizing the potential for accidental ignition; 2) enhanced structural integrity, reducing losses during transit and maximizing resource utilization; and 3) their compact form facilitates efficient storage and reprocessing for easy handling, storage and recycling.

Commonly used binders include molasses and lime. These natural substances promote cohesion among powdered particles, aiding in briquette formation. However, their effectiveness may vary based on the specific mineral composition among other factors.

Polyvinyl alcohol (“PVOH” or “PVA”) may also be used in binder formulations for briquettes, as is discussed in EP3497189B1 by Metcalfe, describing (i) a particulate material selected from a carbonaceous material, metal, metal ore, mineral waste or a mixture thereof; and (ii) a binder, the binder comprising (a) 0.01 to 0.8% by weight of the briquette at least partially saponified polyvinyl alcohol (PVA) and (b) 0.01 to 1.0% by weight of the briquette of an alkali metal alkyl siliconate or polyalkylsilicic acid. With respect to the PVOH, Metcalfe describes the PVA has a degree of saponification of at least 80%, typically at least 85%, at least 90%, at least 95%, 98%, 99% or 100% saponification, and is utilized as a solution in water.

However, providing a PVOH solution in water poses a few challenges, including the fact that shipping pre-solubilized PVOH formulations is more expensive due to the added weight of the water. Further, if PVOH is shipped in its dry resin form as ground up particles, for example, then the end-user facility must use a stirring or cooking apparatus to fully dissolve PVOH into solution for use in a briquette binder formulation, which requires labor and equipment maintenance.

Hence, it would be desirable to provide a PVOH-based briquette binder composition or formulation, and method relating to the same, that does not require pre-dissolved solutions of the PVOH, and that furthermore results in a briquette having improved moisture resistance, mechanical strength and integrity, and other desirable properties.

BRIEF SUMMARY

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

In one aspect, a slurry composition for forming powdered mineral briquettes may comprise 4 wt % to 20 wt % of polyvinyl alcohol (PVOH) granules having a particle size distribution of less than 420 μm, 5 wt % to 9 wt % water, and a remainder comprising powdered mineral, optionally with one or more additives, wherein the total composition is 100 wt % and the PVOH granules are not pre-solubilized.

In another aspect, a method of forming powdered mineral briquettes may comprise mixing PVOH granules having a particle size distribution of less than 420 μm with powdered minerals and water to form a homogeneous slurry comprising 5 wt % to 9 wt % water and 4 wt % to 20 wt % PVOH, followed by molding and compression to shape the slurry into briquettes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A illustrates briquette green strength as a function of PVOH binder particle size distribution according to an aspect of the present disclosure.

FIG. 1B illustrates briquette Green Strength as a function of PVOH binder particle size distribution according to an aspect of the present disclosure.

FIG. 2A is a schematic view of an apparatus for testing the compressive strength of a powdered mineral briquette.

FIG. 2B illustrates briquette maximum compressive strength as a function of PVOH binder particle size distribution according to an aspect of the present disclosure.

FIG. 3 illustrates briquette maximum compressive strength as a function of PVOH binder loading level according to an aspect of the present disclosure.

FIG. 4 illustrates briquette maximum compressive strength as a function of PVOH binder molecular weight according to an aspect of the present disclosure.

FIG. 5 illustrates briquette maximum compressive strength as a function of PVOH binder degree of hydrolysis according to an aspect of the present disclosure.

FIG. 6 illustrates briquette maximum compressive strength as a function of PVOH binder formulation water content according to an aspect of the present disclosure.

FIG. 7 illustrates average briquette weight loss after water exposure as a function of PVOH binder loading according to an aspect of the present disclosure.

FIG. 8 illustrates average briquette weight loss after water exposure as a function of PVOH binder loading and molecular weight according to an aspect of the present disclosure.

FIG. 9 illustrates average briquette weight loss after water exposure as a function of PVOH binder particle size according to an aspect of the present disclosure.

FIG. 10 illustrates average briquette weight loss after water exposure as a function of PVOH binder degree of hydrolysis according to an aspect of the present disclosure.

DETAILED DESCRIPTION

Disclosed herein is an improved PVOH binder composition and method for powdered minerals. Powdered minerals or mineral wastes may include mill scale, mill sludges, manufacturing slags, mining dust, power plant ash/slags, fines from ores or other metal containing wastes. The metal or metal ore mineral waste may include but is not limited to copper, manganese, platinum, vanadium, beryllium, gold, silver, lead, nickel, zinc, iron, titanium, cadmium, chromium, tin, uranium, molybdenum, or mixtures thereof, or elemental metals in the form of oxides or silicates, for example.

In one aspect, a slurry composition for forming powdered mineral briquettes may comprise 4 wt % to 20 wt % of polyvinyl alcohol (PVOH) granules having a particle size distribution of less than 420 μm, 5 wt % to 9 wt % water, and a remainder comprising powdered mineral, optionally with one or more additives, wherein the total composition is 100 wt % and the PVOH granules are not pre-solubilized.

In another aspect, the slurry composition may include PVOH granules having a particle size distribution of less than 250 μm.

In another aspect, the slurry composition may include PVOH granules having a particle size distribution between 250 μm and 420 μm.

In another aspect, the PVOH granules may have a particle size distribution ranging from 180 μm to 250 μm.

In another aspect, the PVOH granules may exhibit a molecular weight between 15,000 g/mol and 210,000 g/mol.

In a further aspect, the slurry composition may comprise PVOH granules having a degree of hydrolysis between 72% and 96.5%. In another aspect, the degree of hydrolysis may fall within the range of 82% to 96.5%. In another aspect, the PVOH granules may exhibit a degree of hydrolysis ranging from 87% to 96.5%.

In another aspect, the one or more additives of the slurry composition may comprise starch, which may not be pre-solubilized.

In some aspects, the slurry composition may include PVOH granules with a degree of hydrolysis above 96.5%.

In yet another aspect, the starch component may comprise partially hydrolyzed starch.

In one aspect, a briquette formed from the slurry composition may exhibit a green strength pass rate of at least 60% as determined by the Green Strength Test.

In another aspect, the green strength pass rate of the briquette may reach 100% when the composition includes PVOH granules having a particle size distribution of less than 250 μm.

In some cases, the briquette may exhibit a compressive strength of at least 2.7 MPa as determined by the Compressive Strength Test.

In another aspect, the briquette may show an average weight loss ranging from about 0.6% to about 12.6% following exposure to water as determined by the Water Exposure Test.

In one aspect, a method of forming powdered mineral briquettes may comprise mixing PVOH granules having a particle size distribution of less than 420 μm with powdered minerals and water to form a homogeneous slurry comprising 5 wt % to 9 wt % water and 4 wt % to 20 wt % PVOH, followed by molding and compression to shape the slurry into briquettes.

In another aspect, the method may utilize PVOH granules having a particle size distribution of less than 250 μm.

In another aspect, the method may include PVOH granules with a molecular weight between 15,000 g/mol and 210,000 g/mol.

In yet another aspect, the method may involve PVOH granules with a degree of hydrolysis ranging between 72% and 96.5%.

The following powdered mineral composition of TABLE 1 was used to prepare the samples described further below.

	TABLE 1
	Element	% of composition

	Nickel	13.15
	Chromium	6.3
	Iron	51.16
	Copper	0.41
	Molybdenum	1.19
	Manganese	0.07
	Cobalt	1.75
	Vanadium	0.05
	Tungsten	0.25
	Niobium	0.25
	Phosphorus	0
	Carbon	1.32
	Sulfur	0.22
	Tin	0.02
	PF	23

This composition is exemplary of what is often used in stainless steel production, for example. The particle size distribution of the powdered mineral composition was less than an 8 mm diameter, but the formulations and techniques of the present disclosure will work with larger particle sizes and ranges, and is not limited to the specific mineral formulation of TABLE 1.

To make briquettes, first a masterbatch was prepared mixing the powdered mineral composition of TABLE 1 with water and dry PVOH granules as a binder. The PVOH resins tested and described further herein are available from Sekisui Specialty Chemicals America LLC, a commercial supplier, and are described as follows in TABLE 2, PVOH Products. All the resins listed are homopolymers of PVOH. All polymer molecular weights referred to in the present disclosure are number average molecular weights. Viscosity was measured in a 4% aqueous solution at 20° C., and pH was measured in a 4% aqueous solution. In some cases, “S” grades of each Selvol product were used or indicated in the results further below, meaning the particle size of this material is <180 μm or <80 MESH U.S. STD, in which case the letter S follows each PVOH Product designation.

TABLE 2
PVOH	Hydrolysis	Viscosity		Molecular Weight
Product	(%)	(cP)	pH	(Mn) g/mol
Selvol 205	87-89	5.2-6.2	4.5-6.5	15,000-20,000
Selvol 523	87-89	23-27	4.5-6.5	85,000-95,000
Selvol 540	87-89	45-55	4.5-6.5	120,000-130,000
Selvol 575	86-89	65-85	5.0-7.0	200,000-210,000
Selvol 425	95.5-96.5	27-31	4.5-6.5	80,000-90,000
Selvol 325	98.0-98.8	28-32	5.0-7.0	75,000-85,000
Selvol E707	70-74	6-10	4.0-6.5	80,000-90,000
Selvol E635	78.5-81.5	32-38	4.0-6.5	85,000-95,000

To control for particle size distribution (PSD) of PVOH binders used in producing various samples, dry PVOH granules were sieved through mesh screens as is known in the art, for example, 10 mesh (2000 μm), 14 mesh (1410 μm), 20 mesh (840 μm), 40 mesh (420 μm), 60 mesh (250 μm), 80 mesh (180 μm), and 100 mesh (150 μm). “Particle size distribution” or PSD as used herein, including in phrases such as “particle size distribution of less than X μm” and “particle size distribution of between X μm and Y μm,” refer to the sizing of dry PVOH granules obtained via sieve-based fractionation. Specifically, PVOH granules are sieved through mesh screens with known aperture sizes, such as 40 mesh (420 μm), 60 mesh (250 μm), or combinations thereof. Granules retained below a 40 mesh screen are considered to have a particle size distribution of less than 420 μm. Similarly, granules passing through a 40 mesh screen but retained above a 60 mesh screen may be described as having a particle size distribution between 250 μm and 420 μm. This sieving practice is well understood in the art and ensures that the particle size distribution corresponds to the aperture size of the final screen through which the granules pass.

Masterbatch samples were prepared by combining the dry PVOH binder granules (not pre-solubilized), water, and the powdered minerals to create a slurry, and homogenizing in a Hobart mixer stirred at 200 rpm and mixed for a period of about 2 to 10 minutes to ensure a homogeneous mixture.

Briquettes were prepared by placing the homogeneous mixture into a stainless steel pre-mold cylinder and applying a force of 10,000 pounds-force (lbf) or about 44.5 kN using a Carvel Model 4126 hydraulic piston press. Resulting sample briquettes had a diameter of 40 mm, height of 22 mm, and were shaped as a puck with circular top and bottom and an average weight of about 100 grams.

The briquettes were then subjected to Green Strength testing (described below) to evaluate their structural integrity before curing. Briquettes that passed the Green Strength Test were cured under two different conditions: some were cured at ambient room temperature for 7 days (“air cured”), while others were cured in an oven set at 105° C. for 2 hours (“oven cured”). Dried briquettes were conditioned for 24 hours at 23° C. and 50% relative humidity (RH) prior to further testing.

Green Strength Test

Sample briquettes were prepared according to the methods described above, and according to the formulations provided in TABLE 3 below, all using Selvol 540 (“S540”), air cured, and utilizing PVOH having varied particle size distributions (PSD) to test the effect on Green Strength. Particle size distributions were achieved using mesh screen filters as described above, and were compared to a standard PSD of PVOH that was unscreened (“std PSD”).

	TABLE 3
	Powdered		PVOH		Green Strength

Sample	mineral	Water	PVOH	Loading	PSD	# passed/
ID	wt. (g)	(g)	Binder	(wt %)	μm	total	% passed

222.17C	610.10	40.20	S540	1.50%	<1450	2/6	33%
222.17B	610.07	40.94	S540	1.50%	<840	2/6	33%
222.17D	611.15	40.50	S540	1.50%	<420	4/6	67%
222.19E	610.00	40.22	S540	1.50%	<250	6/6	100%
222.19F	610.68	41.13	S540	1.50%	>840	0/6	0%
222.19G	609.95	40.90	S540	1.50%	840 >	2/6	33%
					X > 420
222.19H	609.32	40.39	S540	1.50%	420 >	6/6	100%
					X > 250
222.19I	610.10	40.13	S540	1.50%	250 >	6/6	100%
					X > 180
222.21J	612.60	43.76	S540	1.50%	std PSD	1/6	17%
222.17A	610.10	40.10	S540S	1.50%	<180	6/6	100

Green Strength was tested by dropping each sample briquette from a controlled height of 2 meters onto a solid concrete floor surface. A briquette was determined to pass the test if it substantially held its integrity and shape, with no fractures through the body of the briquette, no splitting, and only minor chipping or loss of material off the surface of the briquette. This test simulates the conditions briquettes may face when coming off of a conveyor and dropped into a container for curing, shipping or subsequent use, for example.

As can be appreciated from the results of TABLE 3 as also shown in FIG. 1A, briquettes using a PVOH binder having a particle size distribution of less than 420 μm performed the best, with at least a 60% Green Strength pass rating, and using PVOH particles sizes of less than 250 μm resulted in a surprising 100% pass rating.

As can be appreciated from the results of TABLE 3 as also shown in FIG. 1B, briquettes using PVOH binder granules having a particle size distribution between 250 μm and 420 μm also had a 100% Green Strength pass rating, as did the particle size distribution of between 180 μm and 250 μm. In contrast, PVOH granules having a standard particle size distribution had less than a 20% pass rating. PVOH granules having particle size distributions greater than 840 μm, as well as a PSD of 94% particles greater than 840 μm, both resulted in briquettes that failed all Green Strength Tests. While these results suggest enhanced performance at narrower PSD thresholds, it may be appreciated that PVOH granules with a PSD between 420 μm and 840 μm, particularly those nearer to 420 μm, may also yield acceptable green strength in certain applications or formulations. This broader range may be suitable in formulations where performance tolerances vary or where other compositional factors compensate for granule size differences, including but not limited to the use of additives such as co-binders described further herein.

Accordingly, it was surprisingly discovered that briquettes having good Green Strength could be obtained by optimizing the particle size distribution or PSD of the PVOH binder granules used in the powdered mineral slurry composition, and that furthermore such PVOH did not have to be used as a pre-solubilized solution in order to achieve such results.

Compressive Strength Test

The briquette samples of TABLE 3 formulations were generated both via the air cured and oven cured methods as described above and utilizing PVOH binders having varying particle size distributions to determine the effect on compressive strength.

Compressive Strength Test: To test the compressive strength, an Instron Model 5965 attached with 5 kW load cell was equipped with the system of FIG. 2A, showing a sample briquette 202, a splitter 204, a top plate 206, a bottom plate 208, and a force vector 210 applied by the Instron. The splitter 204 comprised a hexagonal 12 mm allen wrench (hex key). A constant force vector at a rate of 20 cm/min was applied onto the splitter until the briquette split resulting in a maximum compressive recorded value.

The results of the testing are shown in TABLE 4A for air cured, and TABLE 4B for oven cured below, as well as visualized in FIG. 2B.

TABLE 4A
	Compressive Stress at Maximum
Experiment	Comp. Load - Air Cured (Mpa)

ID	Mean	std	Min	Max	Range

222.17C	2.44289	0.25337	2.20707	2.93282	0.72557
222.17B	2.27997	0.46686	1.48429	2.72157	1.23728
222.17D	3.17680	0.17905	2.94252	3.38063	0.4381
222.19E	3.81976	0.14721	3.67837	4.01171	0.33335
222.19F	0.19511	0.08867	0.07453	0.30223	0.22769
222.19G	2.55392	0.51981	1.74773	3.01064	1.26291
222.19H	3.30143	0.21025	3.01706	3.51856	0.5015
222.19I	3.83547	0.11045	3.68864	3.97018	0.28154
222.21J	2.4963	0.33951	2.15679	2.83581	0.67902
222.17A	3.79611	0.18814	3.61046	3.92724	0.31678

TABLE 4B
	Compressive Stress at Maximum
Experiment	Comp. Load - Oven Cured (Mpa)

ID	Mean	std	Min	Max	Range

222.17C	2.11553	0.44009	1.97795	2.36154	0.38359
222.17B	2.00921	0.60054	1.69965	2.46211	0.76246
222.17D	3.20054	0.35788	2.95164	3.28441	0.33277
222.19E	3.66127	0.24476	3.41651	3.90603	0.48952
222.19F	0.12261	0.11006	0.09542	0.26055	0.16513
222.19G	2.26694	0.62211	2.19154	2.44577	0.25423
222.19H	3.29016	0.367751	2.99655	3.33166	0.33511
222.19I	3.64742	0.22219	3.42523	3.86961	0.44438
222.21J	2.85513	0.08712	2.78744	2.95343	0.16599
222.17A	3.422098	0.19322	3.27567	3.64025	0.36458

In FIG. 2B, air cured results are shown in solid bars, and oven cured in hatched bars. FIG. 2B further shows a dotted horizontal line which represents a target value for desired maximum compressive strength in the industry, of at least about 2.7 Mpa, considered to be suitable for briquettes that can withstand transportation and other stresses. As shown in the TABLES above and FIG. 2B, using a PVOH binder granules having a PSD of less than 420 μm surprisingly resulted in briquettes having adequate compression strength, superior to the industry expectation.

Effect of PVOH Binder Loading %

Briquette samples were prepared with the formulations of TABLE 5 below, wherein the PVOH binder loading % with respect to weight of powdered mineral was varied from 0.50 wt % to 5.00 wt %.

	TABLE 5
	Powdered		PVOH		Green Strength

Experiment	mineral	Water	PVOH	loading	PSD	# passed/
ID	wt. (g)	(g)	Binder	(wt %)	μm	total	% passed

222.21L	609.38	40.00	S540	0.50%	<250	0/6	0%
222.21M	609.40	41.21	S540	0.75%	<250	5/6	83%
222.21N	614.06	42.05	S540	1.00%	<250	6/6	100%
222.19E	610.00	40.22	S540	1.50%	<250	6/6	100%
222.22O	607.54	43.30	S540	2.00%	<250	6/6	100%
222.22P	602.00	46.90	S540	3.00%	<250	6/6	100%
222.22Q	589.00	78.50	S540	5.00%	<250	2/2	100%

The results of the compressive strength testing are shown in TABLE 5A for air cured, and TABLE 5B for oven cured below, as well as visualized in FIG. 3.

TABLE 5A
	Compressive Stress at Maximum
Experiment	Comp. Load - Air Cured (Mpa)

ID	Mean	std	Min	Max	Range
222.21L	—	—	—	—	—
222.21M	2.99524	0.49634	2.32238	3.19675	0.87438
222.21N	3.26030	0.09586	3.15758	3.3474	0.18981
222.19E	3.81976	0.14721	3.67837	4.01171	0.33335
222.22O	3.45371	0.07857	3.4068	3.54441	0.13761
222.22P	3.43655	0.03681	3.39768	3.49341	0.09573
222.22Q	3.01158	0.03634	2.98588	3.03728	0.051

TABLE 5B
	Compressive Stress at Maximum
Experiment	Comp. Load - Oven Cured (Mpa)

ID	Mean	std	Min	Max	Range

222.21L	—	—	—	—
222.21M	3.01663	0.61132	2.40531	3.62795	1.22264
222.21N	3.19557	0.04335	3.15222	3.23892	0.08670
222.19E	3.66127	0.24476	3.41651	3.90603	0.48952
222.22O	3.34082	0.16634	3.17448	3.50716	0.33268
222.22P	3.22861	0.30112	2.92749	3.52973	0.60224
222.22Q	2.88837	0.08224	2.80612	2.97061	0.164481

In FIG. 3, air cured results are shown in solid bars, and oven cured in hatched bars. FIG. 3 further shows a dotted horizontal line which represents a target value for desired maximum compressive strength in the industry, of at least about 2.7 Mpa, considered to be suitable for briquettes that can withstand transportation and other stresses. As shown in the TABLES above and FIG. 3, using a PVOH binder at loading levels from about 0.75 wt % to 5.00 wt % surprisingly resulted in briquettes having adequate compression strength, superior to the industry expectation. The samples with PVOH loading of 0.50 wt % had insufficient binding strength to form suitable briquettes, whereas briquettes formed from PVOH loading of 5 wt % were somewhat tacky and more difficult to demold, hence this was determined to be a reasonable upper limit for the PVOH loading.

Effect of PVOH Binder Molecular Weight

Briquette samples were prepared with the formulations of TABLE 6 below, wherein different PVOH binders having different molecular weights (see TABLE 2 for molecular weights) were tested and at varying loading percentages.

	TABLE 6
	Powdered		PVOH	PVOH		Green Strength

Experiment	mineral	Water	PVOH	amount	Loading	PSD	# passed/
ID	wt. (g)	(g)	Binder	(g)	(wt %)	μm	total	% passed

222.37.205-4	602.5	42.1	S205S	4.52	0.75%	<180	0/6	0%
222.35A205S	1014.00	68.10	S205S	15.02	1.50%	<180	2/6	33%
222.37.205S-2	607.60	42.60	S205S	12.4	2.00%	<180	3/6	50%
222.37.205-3	601.40	42.16	S205S	18.6	3.00%	<180	6/6	100%
2222.35B523S-1	1012.24	69.31	S523S	7.50	0.75%	<180	2/6	33%
222.35B523S	1015.44	69.31	S523S	15.06	1.50%	<180	5/6	83%
222.37B523S-2	1000.10	70.10	S523S	20.50	2.00%	<180	6/6	100%
222.37523S-3	990.30	71.40	S523S	30.58	3.00%	<180	6/6	100%
222.21M	609.40	41.21	S540	4.65	0.75%	<250	5/6	83%
222.19E	610.00	40.22	S540	9.33	1.50%	<250	6/6	100%
222.22O	607.54	43.30	S540	12.40	2.00%	<250	6/6	100%
222.22P	602.00	46.90	S540	18.60	3.00%	<250	6/6	100%
222.35C575S	1011.35	70.90	S575S	7.53	0.75%	<180	6/6	100%
222.35C575S-1	1011.35	70.90	S575S	15.00	1.50%	<180	6/6	100%
222.237C575S-2	1004.50	74.10	S575S	20.50	2.00%	<180	6/6	100%
222.237C575S-3	990.00	72.00	S575S	30.60	3.00%	<180	6/6	100%

The results of the testing are shown in TABLE 6A for air cured, and TABLE 6B for oven cured below, as well as visualized in FIG. 4.

	TABLE 6A
	PVOH	Compressive Stress at Maximum Comp. Load - Air Cured (Mpa)

Experiment ID	Binder	Mean	std	Min	Max	Range
—	S205S	—	—	—	—	—
222.35A205S	S205S	3.34388	0.28486	3.06091	3.63059	0.56968
222.37.205S-2	S205S	3.86664	0.04316	3.82737	3.91285	0.08549
222.37.205-3	S205S	4.09718	0.41591	3.68665	4.15664	0.46999
2222.35B523S-1	S523S	3.11188	0.08109	3.06428	3.20551	0.14123
222.35B523S	S523S	3.67575	0.0025	3.67294	3.67771	0.00477
222.37B523S-2	S523S	4.12249	0.14941	4.01118	4.2919	0.28071
222.37523S-3	S523S	4.03086	0.12708	3.8891	4.13457	0.24547
222.21M	S540	2.99524	0.49634	2.32238	3.19675	0.87438
222.19E	S540	3.81976	0.14721	3.67837	4.01171	0.33335
222.22O	S540	3.85371	0.07857	3.4068	3.54441	0.13761
222.22P	S540	3.83655	0.03681	3.39768	3.49341	0.09573
222.35C575S	S575S	3.20238	0.12147	3.07227	3.3128	0.24053
222.35C575S-1	S575S	4.22867	0.11172	4.15562	4.35728	0.20166
222.237C575S-2	S575S	4.10568	0.02258	4.08012	4.12291	0.04279
222.237C575S-3	S575S	3.99825	0.1399	3.88467	4.15452	0.26985

	TABLE 6B
	PVOH	Compressive Stress at Maximum Comp. Load - Oven Cured (Mpa)

Experiment ID	Binder	Mean	std	Min	Max	Range
—	S205S	—	—	—	—	—
222.35A205S	S205S	3.04986	0.10236	2.93461	3.133022	0.19561
222.37.205S-2	S205S	3.27873	0.166683	3.16076	3.39670	0.23594
222.37.205-3	S205S	3.05103	0.2062	3.03645	3.06561	0.02916
2222.35B523S-1	S523S	2.9082	0.10376	2.78995	2.98401	0.19407
222.35B523S	S523S	3.08773	0.07314	3.02053	3.6564	0.1451
222.37B523S-2	S523S	3.25208	0.03329	3.22142	3.2875	0.06607
222.37523S-3	S523S	3.35577	0.0477	3.32305	3.41051	0.08745
222.21M	S540	3.01663	0.61132	2.40531	3.62795	1.22264
222.19E	S540	3.66127	0.24476	3.41651	3.90603	0.48952
222.22O	S540	3.34082	0.16634	3.17448	3.50716	0.33268
222.22P	S540	3.22861	0.30112	2.92749	3.52973	0.60224
222.35C575S	S575S	3.03271	0.14774	2.89308	3.1874	0.29432
222.35C575S-1	S575S	4.21516	0.13129	4.10951	4.36215	0.25263
222.237C575S-2	S575S	3.00246	0.05153	2.96387	3.06098	0.0971
222.237C575S-3	S575S	3.1495	0.016905	2.98641	3.29641	0.31075

In FIG. 4, as in previous Figures, a dotted horizontal line represents a target value for desired maximum compressive strength in the industry, about 2.7 Mpa, considered to be suitable for briquettes that can withstand transportation and other stresses. As shown in the TABLES above and FIG. 4, a broad range of PVOH molecular weights are suitable for use as a binder for powdered minerals, including between 15,000 and 210,000 g/mol. This is in contrast with prior methods of using pre-solubilized PVOH, where lower molecular weight grades of PVOH needed to be used to produce a high solids solution such that when adding the solubilized PVOH, enough PVOH would be present to act as a sufficient binder of the powdered minerals. Based on the results above, it was surprisingly discovered that even very high molecular weight grades of PVOH, such as S540 (MW 120,000-125,000 g/mol) or S575S (200,000-210,000 g/mol) could be used to make slurry compositions for producing briquettes that not only pass Green Strength Tests, but also have sufficient compressive strength beyond industry standard requirements.

Effect of PVOH Binder Degree of Hydrolysis

Briquette samples were prepared with the formulations of TABLE 7 below, wherein different PVOH binders having different degrees of hydrolysis (DOH) were tested.

	TABLE 7
	Powdered		PVOH		Green Strength

Experimental	mineral	water	PVOH	DOH	loading	PSD	# passed/
ID	(g)	(g)	Binder	(%)	(wt %)	μm	total	% passed

222.45.1A	1014.00	68.10	E707	72.00	1.50%	<420	4/6	67%
222.45.4D	1015.44	69.31	E635	82.00	1.50%	<420	5/6	83%
222.17D	611.15	40.50	S540	89.00	1.50%	<420	4/6	67%
222.45.2B	610.6	41	S425	96.50	1.50%	<420	6/6	100%
222.45.3C	608.9	45	S325	98.80	1.50%	<420	0/6	0%

As can be seen from the results of TABLE 7, using a PVOH binder having a degree of hydrolysis of 98.8% did not form suitable briquettes from the slurry compositions. In other words, using PVOH binders with DOH higher than intermediate grades of 72%-96.5% didn't provide adequate binding strength because of the difficulty hydrating the PVOH granules.

The results of the compressive strength testing are shown in TABLE 7A for air cured, and TABLE 7B for oven cured below, as well as visualized in FIG. 5 (air cured results are shown in solid bars, and oven cured in hatched bars).

TABLE 7A
Experiment	PVOH	Compressive Stress at Maximum Comp. Load - Air Cured (Mpa)

ID	Binder	Mean	std	Min	Max	Range

222.45.1A	E707	3.67734	0.06166	3.63275	3.71994	0.0872
222.45.4D	E635	3.39145	0.20016	3.09116	3.48684	0.39568
222.17D	S540	3.17680	0.17905	2.94252	3.38063	0.4381
222.45.2B	S425	3.31017	0.03675	3.28418	3.33616	0.05198
222.45.3C	S325	—	—	—	—	—

TABLE 7B
Experiment	PVOH	Compressive Stress at Maximum Comp. Load - Oven Cured (Mpa)

ID	Binder	Mean	std	Min	Max	Range

222.45.1A	E707	2.38005	0.29594	2.17079	2.58931	0.41853
222.45.4D	E635	3.05757	0.16224	2.96166	3.20131	0.23965
222.17D	S540	3.20054	0.35788	2.95164	3.28441	0.33277
222.45.2B	S425	2.98143	0.07321	2.92966	3.03319	0.10353
222.45.3C	S325	—	—	—	—	—

In FIG. 5, as in previous Figures, a dotted horizontal line represents a target value for desired maximum compressive strength in the industry, about 2.7 Mpa, considered to be suitable for briquettes that can withstand transportation and other stresses. As shown in the TABLES above and FIG. 5, a broad range of PVOH DOH is suitable for use as a binder for powdered minerals, including between 72%-96.5% DOH.

Effect of Free Water/Moisture of Powdered Mineral Slurries

Briquette samples were prepared with the slurry compositions of TABLE 8 below, wherein the amount of water added to the slurry and PVOH concentration was varied to determine whether the PVOH binders and methods of the present disclosure could be effectively used despite the natural or inherent variations that occur in powdered mineral free water content or moisture levels.

	TABLE 8
	PVOH		Green Strength	PVOH

Experiment	Water	PVOH	loading	PSD	# passed/		Conc.
ID	(%)	Binder	(wt %)	μm	total	% passed	(%)

222.39.1	4.00%	S540	1.00%	<250	0/6	0%	25.3%
222.39.2	4.50%	S540	1.00%	<250	0/6	0%	22.5%
222.39.3	5.00%	S540	1.00%	<250	6/6	100%	20.2%
222.39.4	6.00%	S540	1.00%	<250	6/6	100%	17.0%
222.39.5	7.00%	S540	1.00%	<250	6/6	100%	14.5%
222.41.6	8.00%	S540	1.00%	<250	6/6	100%	12.6%
222.41.7	9.00%	S540	1.00%	<250	6/6	100%	11.2%
222.41.8	10.00%	S540	1.00%	<250	0/6	0%	10.1%

As can be appreciated from the results of TABLE 8, a water content of between 5 wt % and 9 wt % was optimal for forming briquettes, whereas below 5 wt % resulted in a slurry too dry to form briquettes, and above 9 wt % resulted in a slurry too wet to form briquettes.

The results of the compressive strength testing are shown in TABLE 8A for air cured, and TABLE 8B for oven cured below, as well as visualized in FIG. 6 (air cured results are shown in solid bars, and oven cured in hatched bars).

	TABLE 8A
	PVOH

Experiment

Water

Compressive Stress at Maximum Comp. Load - Air Cured (Mpa)

Conc.

ID	(wt %)	Mean	std	Min	Max	Range	(wt %)

222.39.1	4.00%	—	—	—	—	—	25.3%
222.39.2	4.50%	—	—	—	—	—	22.5%
222.39.3	5.00%	3.36448	0.12039	3.22547	3.43551	0.21004	20.2%
222.39.4	6.00%	3.75649	0.10028	3.66333	3.86264	0.1993	17.0%
222.39.5	7.00%	3.69381	0.07185	3.64312	3.77604	0.13292	14.5%
222.41.6	8.00%	3.53701	0.13206	3.44441	3.68823	0.24392	12.6%
222.41.7	9.00%	3.60684	0.16265	3.41951	3.7122	0.04778	11.2%
222.41.8	10.00%	—	—	—	—	—	10.1%

	TABLE 8B
	PVOH

Experiment

Water

Compressive Stress at Maximum Comp. Load - Oven Cured (Mpa)

Conc.

ID	(wt %)	Mean	std	Min	Max	Range	(wt %)

222.39.1	4.00%	—	—	—	—	—	25.3%
222.39.2	4.50%	—	—	—	—	—	22.5%
222.39.3	5.00%	3.16642	0.20995	2.95647	3.37637	0.41990	20.2%
222.39.4	6.00%	3.66421	0.11114	3.55307	3.77535	0.22228	17.0%
222.39.5	7.00%	3.58441	0.01321	3.57120	3.59762	0.02642	14.5%
222.41.6	8.00%	3.50694	0.14877	3.35817	3.65571	0.29754	12.6%
222.41.7	9.00%	3.61003	0.18502	3.42501	3.79505	0.37004	11.2%
222.41.8	10.00%	—	—	—	—	—	10.1%

In FIG. 6, as in previous Figures, a dotted horizontal line represents a target value for desired maximum compressive strength in the industry, of at least about 2.7 Mpa, considered to be suitable for briquettes that can withstand transportation and other stresses. As shown in the TABLES above and FIG. 6, the PVOH binders and slurry compositions and methods of the present disclosure are suitable and flexible to produce briquettes having sufficient Green Strength and compressive strength for a wide range of powdered mineral free water or moisture content, allowing the use of between 5 wt % to 9 wt % total water in the slurry mixture by varying the concentration of PVOH binder used, such as between about 20.2 wt % to 11.2 wt %. Accordingly, regardless of the amount of free water content of powdered mineral sources, as long as the final slurry is brought up to between about 5 wt % to 9 wt % total water, then suitable briquettes may be made utilizing the PVOH binders and methods disclosed herein.

Durability of Briquettes Against Water Exposure Test

Briquettes made from powdered mineral byproducts are often exposed to the elements such as rain during transport on open bed trucks, barges and other points of exposure. Accordingly, durability of briquettes made according to the PVOH binder formulations and methods of the present disclosure were tested as follows.

Water Exposure Test: briquettes air cured for 7 days at room temperature as described in the methods above were immersed in 100 ml of tap water in beakers and left to stand at room temperature for 24 hours. Following this period, the briquettes were taken out, gently rinsed to eliminate loose or detached pieces, and subsequently redried in a 100° C. oven for 3 days to eliminate any remaining water. The final weight of the briquettes was then measured and compared against the starting weight of the briquettes to determine the % of weight loss that occurred as a result of the water exposure.

TABLE 9 below shows the Water Exposure Test results as a function of PVOH binder loading % for Selvol 540, PSD of 60 mesh (250 μm).

	TABLE 9
	Experiment	PVOH Loading	Avg. Weight	STD Dev
	ID	(wt %)	Loss (%)	(%)

	222.25A1	0.75%	2.11%	0.42%
	222.25B1	1.25%	2.16%	0.23%
	222.25J1	1.50%	0.60%	0.14%
	222.25C1	2.00%	2.27%	0.03%
	222.25D1	3.00%	3.45%	0.96%
	222.25-E1	5.00%	6.20%	0.26%

FIG. 7 is a graph of the results of TABLE 9. Though not shown in TABLE 9 or FIG. 7, commercial powdered mineral binder compositions utilizing molasses and lime typically have an average weight loss of 19.1%+/−4.86% when subjected to the Water Exposure Test. Accordingly, as can be appreciated from the results, markedly improved performance was achieved with all of the tested loading amounts of 0.75 wt % to 5.00 wt % PVOH binder, resulting in average weight loss of between about 0.6% to about 6.2%.

To determine the effect of molecular weight of PVOH binders versus water resistance, briquettes were made according to the method described above, including PSD of 60 mesh (250 μm), but using different molecular weight PVOH binders, and at varying loading percentages, with the results of the Water Exposure Test shown in TABLE 10 below and FIG. 8. Molecular weights of each PVOH Binder are shown with reference to TABLE 2 described previously.

	TABLE 10
	PVOH	PVOH Loading	Avg. Weight	STD Dev.
	Binder	(wt %)	Loss (%)	(%)

	S205S	0.75%	—	—
		1.50%	12.62%	2.23%
		2.00%	5.20%	0.10%
		3.00%	4.35%	0.66%
	S523S	0.75%	4.85%	0.02%
		1.50%	3.93%	0.27%
		2.00%	3.40%	0.09%
		3.00%	2.94%	0.44%
	S540	0.75%	2.11%	0.42%
		1.50%	0.60%	0.14%
		2.00%	2.27%	0.03%
		3.00%	3.46%	0.96%
	S575S	0.75%	2.67%	0.34%
		1.50%	2.43%	0.10%
		2.00%	2.81%	0.09%
		3.00%	2.90%	0.12%

As can be appreciated from the results of TABLE 10 and FIG. 8, all of the PVOH binders had an average weight loss of between about 0.6% to about 12.6%, and performed better than a molasses and lime briquette standard (average weight loss of 19.1%+/−4.86%), however, higher molecular weight grades of PVOH binders such as S523S, S540 and S575S performed better than the lower molecular weight grade of S205S, for example. At 0.75 wt % loading, S205S did not form a suitable briquette for testing.

To determine the effect of particle size distribution of PVOH binders versus water resistance, briquettes were made according to the method described above using Selvol 540 at 1.5 wt % loading but using different particle sizes. The results of the Water Exposure Test are shown in TABLE 11 below and FIG. 9.

	TABLE 11
	Experiment	PSD		Avg. Weight	STD.
	ID	(um)		Loss (%)	Dev. (%)

	222.25G1	>1410	um	100.00%	—
	222.25F1	<1410	um	35.34%	31.74%
	222.43Z1	<840	um	21.67%	24.56%
	222.43Y1	<420	um	2.82%	3.26%
	222.25J1	<250	um	0.46%	0.60%
	222.17A	<180	um	1.30%	1.30%

As can be appreciated from the results, using a PVOH binder particle size distribution of less than 420 μm surprisingly resulted in briquettes having minimal weight loss after being subjected to the Water Exposure Test.

To determine the effect of degree of hydrolysis of PVOH binders versus water resistance, briquettes were made according to the method described above using PVOH binders having varying degrees of hydrolysis, all with a particle size distribution of less than 420 μm and a loading of 1.5 wt %. The results of the Water Exposure Test are shown in TABLE 12 below and FIG. 10.

TABLE 12
Experiment ID	PVOH Binder	DOH	Avg. Weight Loss (%)

222.45.1A	E707	72%	20.93%
222.45.4D	E635	82%	12.72%
222.17D	S540	87%	0.60%
222.45.2B	S425	96.5%	0.39%
222.45.3C	S325	98.8%	—

As can be appreciated from the results, using a PVOH binder granules having a DOH of at least 87% but lower than 98.8% was optimal for achieving good water resistance and minimal weight loss. Using a high DOH of 98.8% did not allow for the formation of suitable briquettes for testing. A DOH of 82% was less optimal, but still performed better than the commercial standard briquettes formulated with molasses and lime, which has an average weight loss of 19.1%+/−4.86%. Using a PVOH binder having a low DOH of 72% resulted in performance comparable to commercial standard briquettes.

Typically, waterproofing techniques are employed, such as coating briquettes with latex-based materials, to improve water resistance. However, based on the results of the Water Exposure Tests above, it was surprisingly discovered that the PVOH binder formulations and methods of the present disclosure were able to achieve exceptional water resistance without the need for any additional coating chemistries or techniques. Further, such briquettes according to the present disclosure exhibit high performance under other testing methods, including the Green Strength Tests and Compressive Strength Tests.

Use of Co-Binders with High Degree of Hydrolysis PVOH

As described with reference to TABLES 7, 7A, 7B and 12 of the present disclosure, use of PVOH binders having a high degree of hydrolysis of 98.8% did not form suitable briquettes and didn't provide adequate binding strength to pass the Green Strength test. Accordingly, a co-binder was tested for use with high DOH PVOH, forming a briquette for testing using the methods described previously in the present disclosure, and using the following formulation of TABLE 13 for the slurry composition:

	TABLE 13
	Powdered		PVOH	Co-binder	PVOH		Green Strength

Experiment	mineral	Water	amount	amount	Loading	PSD	# passed/
ID	wt. (g)	(g)	(g)	(g)	(wt %)	μm	total	% passed
222.125B	400	31	3	3	0.75	<120	4/4	100%

S325 having a DOH of 98.8% was used as the PVOH binder, and dextrin was used as the co-binder. Dextrin was used as the co-binder because it has a low DOH and is inexpensive and readily available, but any low molecular weight carbohydrate, partially hydrolyzed starch or modified starch may be used alone or in combination with dextrin.

A suitable briquette was formed from the slurry composition, and all the briquette samples passed the Green Strength Test. The cured maximum compressive strength of the briquette was 3.35 MPa. When subjected to the Water Exposure Test using the methods described previously, after 24 hours the briquette experienced a 0.35% weight loss.

In view of these results, it was surprisingly discovered that a PVOH having a high DOH such as 98.8% could form a commercially suitable briquette with powdered minerals. This was further surprising because the co-binder was added in the form of a powder (i.e., not pre-solubilized) with the dry PVOH granules and powdered minerals to form a slurry in water, in contrast with prior methods that rely on pre-dissolving PVOH and other components in solution before adding to the powdered minerals. As described previously, this method allows for better and more consistent briquette formation regardless of the amount of free water content of the powdered mineral sources, as long as the final slurry is brought up to between about 5 wt % to 9 wt % total water. The co-binder, having a lower DOH, is easier to solubilize in the slurry which aids the high DOH PVOH granules to dissolve just enough to bind the powdered minerals into briquettes. Mixing with added heat would also aid in solubilizing the high DOH PVOH for more effective binding, and such heat may come from the friction generated by the mixer used, for example.

The co-binder may be added in an amount equal to about 50% of the PVOH binder granules in the slurry composition. Based on the results and discussion with reference to TABLE 8, it was determined that the use of between about 5 wt % to 9 wt % total water in the slurry mixture and about 11 wt % to about 20 wt % of PVOH binder granules resulted in briquettes passing green strength and compressive strength tests. Further, the results and discussion with reference to TABLES 5, 5A and 5B showed using a PVOH binder at loading levels from about 0.75 wt % to 5.00 wt % relative to weight of powdered minerals surprisingly resulted in briquettes having adequate compression strength, superior to the industry expectation. A PVOH binder loading level of 0.75 wt %, would equate to about 4 wt % to 7 wt % of the PVOH binder granules in a slurry composition including the 5 wt % to 9 wt % total water. Accordingly, a suitable range for the PVOH binder granules in such slurry compositions where an additive may optionally be included, such as a co-binder, is from about 4 wt % to a maximum of 20 wt %.

While the invention has been described with reference to exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made, and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof.