Claims:WE CLAIM:
1. A method of dewatering a coal slurry, the method comprising:
treating the coal slurry with a coagulant and surfactant;
adding a flocculant in a treated coal slurry; and
collecting a dense coal slurry left with a treated water.
2. The method as claimed in claim 1, wherein the coal slurry comprises bituminous coal.
3. The method as claimed in claim 2, wherein the bituminous coal is approx. D 80 is -35 micron.
4. The method as claimed in claim 1, wherein the flocculant is Poly acrylamide based.
5. The method as claimed in claim 1, wherein the coagulant is Iron Chloride (FeCl3).
6. The method as claimed in claim 1, wherein the surfactant is cetyl trimethyl ammonium bromide (CTAB).
7. The method as claimed in claim 1, wherein the flocculant added in the coal slurry is 90-125 grams per ton of coal.
8. The method as claimed in claim 1, wherein the coagulant added in the coal slurry is 0.5 – 5 mili grams per ton of coal.
9. The method as claimed in claim 1, wherein the surfactant added in the coal slurry is 0.5 – 5 mili grams per ton of coal.
, Description:DEWATERING OF COAL SLURRY BY PRE-TREATMENT WITH SURFACTANT

TECHNICAL FIELD
[0001] The present disclosure, in general, relates to the development of a combination of reagents for settling of Ultra fine clean coal particles in a High Rate Thickener. In particular, the present disclosure relates to a method of dewatering a coal slurry.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Dewatering of mineral concentrates and tailings is an important part of mining and mineral processing activities. The dewatering is essential because water has become the most critical commodity in any processing plant. Consequently, water must be highly recycled within the processing plants. Thickener and filter units are mostly used for dewatering purpose. After utilization in Thickeners and filter units, most of the process water has been recycled. Around 80% of total process water is said to be recycled by the Thickeners.
[0004] The beneficiation process requires around 300-5 l/ton of ore processed. Accordingly, it is essential to maximize the water recovery by using dewatering techniques.
[0005] Polymeric flocculation finds a wide application for dewatering industries especially involving mineral processing, hydrometallurgy, and water treatment. The polymeric flocculants are added to gravity thickeners to enhance solid liquid separation performance. It is a key step in many processes for effective solid-liquid separation in gravity thickeners.
[0006] Further, in the process of coagulation, the destabilization occurs through charge neutralization by addition of inorganic reagents. After the charge neutralization is over, the small suspended particles adhere together. The resulting slightly larger particles, called micro flocs, are not visible to the naked eye. Inorganic salts such as aluminium and iron salts, silicates and phosphates of sodium are most commonly used as coagulants. In aqueous medium, they ionize and produce highly charged ions to neutralize the charge on the suspended particles. The inorganic hydroxides produce short polymer chains which augment the formation of micro flocs.
[0007] The nature of flocs depends on various factors such as nature of solids (surface chemistry, size, size distribution, shape, density), nature of liquid (viscosity, dielectric constant), nature of suspension (electric charge, pH, ion strength, temperature), and nature of flocculants (chemical properties of main part and chains, molecular weight, molecular weight distribution, electric charge, density of electric charge).
[0008] Long chain polymers when added in small dosage to a suspension of colloidal particles, adsorb onto them in such a manner that an individual chain can become attached to two or more particles thus “bridging” them together. But interestingly this phenomenon is observed up to a particular optimum polymer dosage beyond which flocculation diminishes, a process being known as steric stabilization.
[0009] At lower dosages, there is insufficient polymer to form adequate bridging links between particles. With excess polymer, there is no longer enough bare particle surface available for attachment of segments and the particles become destabilized, which may involve some steric repulsion.
[0010] The main factors that affect coagulation are particle size, surface charge, and water chemistry. The smaller the particle size, the greater total surface area per unit weight of solids, so it is not atypical to see an increase in the dose required to coagulate fine particles. This increase is not linear as small decreases in particle size can result in dramatic increases in coagulant requirements.
[0011] Various approaches have been suggested in the state of the art to perform dewatering of coal using flocculent type on the flocculation mechanism. For instance, Sabah and Cengiz investigated the effects of flocculent type on the flocculation mechanism of coal tailing particles. They obtained the lowest turbidity values for different flocculent types.
[0012] Similarly, the addition of polymer into solution with particles can result in additional attractive forces (Israelachvili 1991). Bridging forces arise when the added polymer adsorbs onto more than one surface, resulting in the aggregation of particles. Bridging forces are commonly used within the minerals industry in order to aggregate particles and increase settling rates.
[0013] Coagulation refers to the aggregation of particles due to the depletion or neutralization of their repulsive forces neutralization of repulsive forces are often performed via pH modification or the addition of low molecular weight (MW) highly charged moieties of opposite charge compared to the particle surface (Verrelli 2008).
[0014] Method for dewatering coal tailings using DADMAC/Vinyl TrialKoxysilane Copolymer as a coagulant is described in US Patent Publication bearing no.US5476522A.
[0015] Hydrophobic Polyelectrolyte Coagulants for Concentrating Coal Tailings in US Patent Publication bearing no.US5330546A.
[0016] Flocculation of Coal fine with Polyelectrolytes and Electrolyte in US Patent Publication bearing no.US4906386A.
[0017] Vinylamine copolymer coagulants for use in coal refuse dewatering in US Patent Publication bearing no.US5622533A
[0018] Starch/cationic polymer combinations as coagulants for the mining industry in US Patent Publication bearing no. US6042732A

OBJECTS OF THE DISCLOSURE
[0019] In view of the foregoing limitations inherent in the state of the art, some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed hereinbelow.
[0020] It is a general object of the present disclosure to establish the optimal conditions for floc formation and determine the optimum settling velocity. Solids recovery was the main purpose for our study and water clarity was of course another important parameter. The parameters chosen for the study was settling rate, overflow water clarity and reagents dosage.
[0021] It is yet another object of the present disclosure to increase the density of under flow of thickener which can be further dewatered using filtration techniques and increase recirculation of clear supernatant water. This has a direct effect on decreasing the use of fresh water in upstream process of Coal beneficiation. Also by pre-treatment of coal slurry with coagulants and surfactants, there will be drastic decline in the consumption of Flocculent dosage.
[0022] It is yet another object of the present disclosure to optimize the reagent consumption in flotation, as a huge amount of ultrafine clean coal is generally recirculated to the upstream process, which increase the consumption of reagents in flotation.

SUMMARY
[0023] This summary is provided to introduce concepts related to a method of dewatering a coal slurry. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0024] In an embodiment, the present disclosure relates to a method of dewatering a coal slurry. The method begins with treating the coal slurry with a coagulant and surfactant, followed with adding a flocculant in a treated coal slurry, and finally collecting a dense coal slurry left with a treated water.
[0025] In an aspect, the coal slurry comprises bituminous coal.
[0026] In an aspect, the bituminous coal is approx. D 80 is -35 micron.
[0027] In an aspect, the flocculant is Poly acrylamide based.
[0028] In an aspect, the coagulant is Iron Chloride (FeCl3).
[0029] In an aspect, the surfactant is cetyl trimethyl ammonium bromide (CTAB).
[0030] In an aspect, the flocculant added in the coal slurry is 90-125 grams per ton of coal.
[0031] In an aspect, the coagulant added in the coal slurry is 0.5 – 5 mili grams per ton of coal.
[0032] In an aspect, the surfactant added in the coal slurry is 0.5 – 5 mili grams per ton of coal.
[0033] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWING
[0034] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and methods that are consistent with the subject matter as claimed herein, wherein:
[0035] FIG. 1 illustrates a method of dewatering a coal slurry in accordance with an embodiment of the present disclosure;
[0036] FIG. 2 illustrates the raw coal settling trend;
[0037] FIG. 3 illustrates settling behaviours when Flocculent is added;
[0038] FIG. 4 illustrates the pre-treatment with Coagulant and then addition of flocculent;
[0039] FIG. 5 illustrates the addition of surfactant; and
[0040] FIGS. 6, 7, and 8 illustrate Fourier Transform Infrared Spectroscopy (FTIR) spectra of Flocculent, Coagulant and Surfactant.

DETAILED DESCRIPTION
[0041] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0042] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0043] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, “consisting” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0044] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0045] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0046] Embodiments explained herein pertain to the development of a combination of reagents for settling of Ultra fine clean coal particles in a High Rate Thickener. As the coal particles are Ultra fine in size (-34µ) and due to their hydrophobic nature, it is very difficult to recover clear water. To do so Flocculants and Coagulants are added in dewatering operations but results were not appreciable. Still around 4-5% of coal is recirculated to upstream process in the process water. Hence, studies are done on different combinations of reagents including Coagulants and Surfactants. A comprehensive settling and dewatering test work was conducted with Clean Coal slurry using several commercial reagents. The reagents were assessed based on their performance with respect to settling rates, overflow water clarity and compaction of the solids. Emphasis was given to the role of reagents in their ability to compact thickener underflow at higher densities so that maximum water could be recovered in the whole process, i.e., from thickener.
[0047] In an aspect, Fine Coal slurry (feed to thickener) with 5% solids was used for various experiments. The particle size distribution analysis suggests that the 80% of the Coal is (-) 34 microns. Poly acrylamide based flocculants were tested for the sample of fine coal slurry. Around 7 (F1, F2, F3, F4, F5, F6 & F7) different reagents were used for this study. Out of the 7 reagents, F1 reagent was selected based on the settling performance in the jar testing apparatus.
[0048] This selected flocculent was tested on pretreated slurry with 5 different Coagulants (C1, C2, C3, C4 & C5) and 4 different Surfactants (S1, S2, S3 & S4). All the combinations of Coagulant and Surfactant were studied. Detailed studies were carried out with these reagents to ascertain the best reagent combination and the maximum clarity achieved. The concentration of flocculants prepared was 0.1% & 100 gpt and it was same for all the reagents and experiments. The concentration of Coagulant and Surfactant used were 1PPM in all the experiments.
Flocculation studies
[0049] Flocculation experiments were carried out with seven different reagents at different dosages to ascertain their settling behaviour and impact on the compaction of the flocs. Settling experiments were performed and the settling rates of the coal fines and unsettled % of fine coal has been compared in Table 01 with the seven different reagents. Reagent F1 showed the best settling rate and good water clarity. The remaining reagents have not shown comparatively good results; this could be due the improper unfolding of the polymer chains due to lack of proper aging time for this set of experimentation. Reagents F6 and F7 showed good settling behavior initially but slowed down considerably and also water clarity was not very good. This was probably due to the formation of loose, fluffy flocs formed by Reagents F6 and F7. This led to higher settling rates initially but as they entered the hindered zone, settling slowed down considerably due to steric hindrance. The optimum dosage for each reagent was found out from this set of experiments. Reagent F1 showed optimum settling behavior at around 100 gpt dosage whereas the optimum dosages for Reagents F6 and F7 were 100 and 200 gpt respectively. The settling rates and % of unsettled coal particles has been shown in Table 01 which also shows that the settling rates are higher for Reagents F6 and F1 but the fact that turbidity of the supernatant water is minimum for F1 reagent, reagent F1 is been selected for further studies. The optimum dosage for the plant condition is about 100 gpt. Hence the next set of experiments were conducted at a common dosage of 100 gpt to find the comparative settling behavior at this dosage.
Flocculent Dosage (gpt) Settling Rate (mm/sec) Unsettled (%)
F1 100 33.76 5
F2 100 29.67 6
F3 100 25.15 8
F4 100 28.72 6
F5 100 26.23 9
F6 100 34.48 8
F7 100 30.43 7
Table 01

Coagulant studies at constant Flocculent dosage
[0050] Coal slurry with 5% solids were prepared for experimentation. Different dosages of different commercial coagulants were added to the slurry to find the effect of the reagent dosages on the compaction of the coal fines. The different coagulants tested were CaCl2, FeCl3, Al2Cl3, Alum & PAC and will be further referred as C1, C2, C3, C4 and C5 respectively. The experiments were conducted at different dosages of these reagents i.e., at 1,2,5,10,50,100 and 200 ppm. The flocculent dosage was kept constant at 100 gpt and the experiments were conducted. Coal slurry was pre-treated with the coagulant and then flocculent was added to study the settling rates and water clarity. Table 02 below shows the settling rates and water clarity with different reagents at optimum dosage of 1 ppm. From the table, it is observed that settling rates have decreased a little compared to first experiment set with only flocculants, But the amount of unsettled fine particles is almost same. Reagent C2 has shown good settling rates and also reasonable decrease in unsettle fine particles. From these experiments reagent C2 has been selected based on settling rate and unsettled fine coal as suitable reagent for further study. As the unsettled Ultra fine particles are still to a greater extent, further experiments were conducted using 4 different Surfactants at two different dosages.
Flocculent Coagulant Dosage (ppm) Settling rate (mm/sec) Unsettled (%)
C1 1 26.5 5
C2 1 31.45 4
F1 C3 1 19.82 6
C4 1 28.19 5
C5 1 22.07 7
Table 02

Selection of Surfactant
[0051] Experiments were carried out to explore the role of surfactants in the settling of Ultra Fine Coal. Four different surfactants were tested and results tabulated The surfactants used in this study will be referred hereafter as S1, S2, S3 and S4. Feed slurry was treated with the selected Coagulant (C2). Then the slurry was again treated with different surfactants at dosages (1 ppm) and the results are tabulated in Table 03. Cationic, anionic and non-ionic surfactants were tested in the experiments and found that best results were found with cationic surfactants S1 and S4. Water clarity is better with S1 compared to S4. From all the above experiments conducted, a combination of three reagents (C2, S1 and F1) was found to be very effective in increasing supernatant water clarity and also decreasing the quantity of unsettled ultrafine particles.
Flocculent Coagulant Surfactant Dosage (ppm) Settling Rate (mm/sec) Unsettled (%)
S1 1 29.46 0.8
F1 C2 S2 1 20.72 4
S3 1 19.64 4.5
S4 1 25.18 1.5
Table 03

[0052] FIGS. 6, 7, and 8 illustrate Fourier Transform Infrared Spectroscopy (FTIR) spectra of Flocculent, Coagulant and Surfactant.
Conclusions:
[0053] Settling studies were conducted with a variety of commercial reagents. Out of the four Surfactants, One Surfactant (cetyl trimethyl ammonium bromide (CTAB)) was selected based on the Jar test results and then detailed settling studies were conducted.
[0054] Coal slurry was pretreated with Coagulant (FeCl3) and then by Surfactant (CTAB). Then Polyacrylamide based polymer was added to achieve the best results based on settling rates and water clarity.
[0055] It was observed that on addition of Surfactant, there is a drastic change in the amount of unsettled coal fines (from 4% to 0.8%) reported in recirculation water from dewatering process.
[0056] Based on the above mentioned studies, the present disclosure proposes a method 100 for dewatering a cloal slurry, in accordance with an embodiment of the present disclosure. FIG. 1 illustrates the method 100 for dewatering a cloal slurry. The order in which the method 100 is described is not intended to be construed as a limitation, and any number of the described method blocks may be combined in any order to implement the method 100, or an alternative method.
[0057] At block 102, the method 100 includes treating the coal slurry with a coagulant and surfactant.
[0058] At block 104, the method 100 includes adding a flocculant in a treated coal slurry.
[0059] At block 106, the method 100 includes collecting a dense coal slurry left with a treated water.
[0060] The execution of the method 100 is represented by way of FIGS. 2-5, wherein FIG. 2 illustrates the raw coal settling trend; FIG. 3 illustrates settling behaviors when Flocculent is added; FIG. 4 illustrates the pretreatment with Coagulant and then addition of flocculent; and FIG. 5 illustrates the addition of surfactant.
[0061] In an aspect, the coal slurry comprises bituminous coal.
[0062] In an aspect, the bituminous coal is approx. D 80 is -35 micron.
[0063] In an aspect, the flocculant is Poly acrylamide based.
[0064] In an aspect, the coagulant is Iron Chloride (FeCl3).
[0065] In an aspect, the surfactant is CTAB.
[0066] In an aspect, the flocculant added in the coal slurry is 90-125 grams per ton of coal.
[0067] In an aspect, the coagulant added in the coal slurry is 0.5 – 5 mili grams per ton of coal.
[0068] In an aspect, the surfactant added in the coal slurry is 0.5 – 5 mili grams per ton of coal.
[0069] Thus, with the implementation of the subject matter described herein, the present disclosure provides a process to increase the density of under flow of thickener which can be further dewatered using filtration techniques and increase recirculation of clear supernatant water. This has a direct effect on decreasing the use of fresh water in upstream process of Coal beneficiation. Also by pre-treatment of coal slurry with coagulants and surfactants, there will be drastic decline in the consumption of Flocculent dosage.
[0070] Further, those skilled in the art can appreciate that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0071] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0072] While the foregoing describes various embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof. The scope of the present disclosure is determined by the claims that follow. The present disclosure is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.