Title of Invention

A PROCESS FOR PREPARATION OF A SURFACE ACTIVE AGENT USEFUL AS CHEMICAL ADDITIVE/ POLYELECTROLYTE

Abstract

A process for the preparation of a surface active agent usefir1 as chemical additive and a polyelectrolyte for the removal of aluminous gangue minerals from ore fines, which comprises treating lignite as mined or after grinding with dilute sulphuric acid, with lignite to sulphuric acid ratio in the range of 1 :5 to 1 : 10 and heating the resuIting mixture, at a temperature of 70-9g0c, for a period in the range of 1-4 hrs, followed by filtration or centrifugation of the mixture as such, washing the resultant solid product with water and mixing it with aqueous sodium hydroxide solution and maintaining the solid to sodium hydroxide ratio in the range of 1 :0.3 to 1 :0.7 and solid to water ratio in the range of 1 :5 to I : 10, heating the resultant mixture at a temperature in the range of 60-98"C, for a period of 1-1 0 hours followed by separation of the liquid product by known methods to obtain the desired product.

Full Text

This invention relates to a process for preparation of a chemical additive/surface active agent/polyelectrolyte suitable for dispersing minerals containing alumina and other related materials having hydroxy and oxy-hydroxy groups in aqueous medium. Particularly, this invention relates to development of a process for preparing a surface active agent capable of dispersing clay and lateritic or similar type of gangue minerals present in ores and minerals. More particularly, this invention relates to development of a process for preparing a surface active agent/chemical additive/polyelectrolyte based on lignite suitable for dispersing alumina containing minerals/clay and/or related minerals present in iron ore fines and slimes by following dispersion-cum-settling technique leading to beneficiation or upgradation of iron ore fines and slimes. In the mineral processing industries, beneficiation and upgradation of low-grade ores and minerals is an essential step for their eventual commercial utilization. Effective liberation, separation and selective dispersion of the gangue minerals and flocculation of the active minerals are the essential prerequisites for upgradation of active minerals. Indian iron ore contains considerable amount of alumina bearing materials. The presence of high amount of alumina affects the productivity of the blast furnace used for extraction of iron. Moreover, it leads to increase in coke, flux rate and slag volume in the blast furnace. Therefore, there is a great necessity for developing suitable methods/techniques for beneficiation of ores and minerals. It has been estimated that one percent of Fe increase in the beneficiated iron ore (concentrate) lead to reduction of the production cost of the hot metal by Rs. 51.46 per ton (Project completion report No. R&D 12:02:1676:91 of Research and Development Centre for Iron & Steel, Steel Authority of India Limited, Ranchi, August 1991) due to increase in production of the hot metal and considerable decrease in consumption of coke, fluxing materials and generation of slag. Indian iron ore contains fine-grained clay and lateritic minerals. It is difficult to remove these gangue minerals and to upgrade/beneficiate the iron ore by adopting the conventional beneficiation techniques as practised in Indian iron ore washeries. The conventional method of beneficiation consists of scrubbing the ore-water slurry under turbulent condition, followed by classification of the slurry using spiral classifier, optionally/additional treatment in jig and dewatering. The practised methods of beneficiation do not alter the Al2O3/Fe and Al2O3/S1O2 ratios of the washed iron ore significantly. The current trend of iron extraction in the blast furnace requires high quality sinter grade iron ore fines (>62 %Fe) and lump (>67.6-68 %Fe) and steel making by direct reduction requires iron ore containing >67.5-68 %Fe. All these factors require development of more effective beneficiation technique. The use of inorganic chemical agents likes sodium carbonate, sodium silicate, sodium hydroxide, sodium pyrophosphate, sodium hexametaphosphate, etc are well known as dispersant in clay beneficiation. These chemical agents are not suitable for selective fiocculation and dispersion towards certain components. Preparation of several polymeric dispersants based on lignosulfonate and the products of formaldehyde, polyacrylamide and modified form of polyacrylamide, alkali metal styrene, sulfonates, bisulphite, terminated oligomer and sodium salt of carboxylated polyelectrolytes have been reported in the patent literature (US patent No. 3898037, 337463,4004939,3594203,3736165,3737383). Some of these polymeric dispersants can disperse clay suitable as coating materials for paper from bulk clay and are used as tanning agents. Most of these polymeric products are however, incompatible towards reasonable amount of polyvalent ions present in the medium and are non-specific in action. The selectivity of these polymeric additives in dispersing alumina containing minerals from lateritic type iron ore and/or hydroxy and oxy-hydroxy containing minerals as associated with Indian iron ore and from high alumina containing iron ore of the world was not disclosed in the patent literatures. Starch and its caustisized products are reported as depressants for iron particle to recover iron value from iron ore (S. Subramanian and K. A. Natarajan, "Floceulation, filtration and selective flocculauon studies on hematite ore tines using starch", Minerals Engineering, 1991,4,587-598; C. L. L. Pinto, A. C. de Araujo and A. E. C. Peres, "The effect of starch, amylose and amylopectin on the depression of oxi-minerals", Minerals Engineering, 1992, 5,469-478; P. K. Weissenborn, L. J. Warren and J. G. Dunn, "Optimisation of selective flocculation of ultrafine iron ore", Int. J. Miner. Process., 1994, 42, 191-213; ; P. K. Weissenborn, L. J. Warren and J. G. Dunn, "Selective flocculation of ultrafine iron ore. 1. Mechanism of adsorption of starch onto hematite", Colloids and Surfaces A: Physicochemical and Engineering Aspect, 1995, 99, 11-27; A. E. C. Peres and M. I. Correa, "Depression of iron oxides with com starches", Minerals Engineering, 1996, 9, 1227-1234). However, compatibility 'of these products towards polyvalent ions usually present in the process water and/or in the ore-slurry media is not known. On the other hand, high cost of corn starch and its allied products and their use may not be techno-economically viable for commercial use for upgradation of iron ore. L. V. Girina and I. E. Sharanova, two Russian authors reported use of sulfonated humates as stabilizing agents in the article, "Stabilization of a clay suspension by sulfonated humates of earthy and dense brown coals, Khim. Tverd. Topi. (Moscow), 1995, 1,68-73; CA 122:269592 (1995)", however the process route is not properly known. In an Indian patent (No. 590NF02, 2002), sulfonation of lignite (C=52.26%, H=5.29%, N=1.28% and S+O=41.17%) is reported using concentrated sulfuric acid (98%) or the like one and subsequent digestion with sodium hydroxide is carried out. In this patent, problem relating to handling during centrifugation and/or reuse of unreacted sulfuric acid for sulfonation of lignite are not mentioned. J. V. Ibarra and J. J. Lazaro reported in Ind. Eng. Chem. Prod. Res. Dev., 1985,24,604-607 sulfonation of Spanish lignite having C = 72.7 wt%, H = 5.1 wt% by using concentrated sulfuric acid and use of the sulfonated lignite as cation exchanger materials. Sulfonation of lignite using dilute sulfuric acid which eliminates all the problems associated with handling, separation of the product from concentrated sulfuric acid etc, and subsequent preparation of alkali salt and its use as a surface active agent/dispersant is not known. A polymeric dispersant as described in Indian patent No. 143850 (1976), prepared by using phenol, formaldehyde and sodium bisulphite as raw materials possesses high compatibility for polyvalent ions and disperses clay and alumina containing minerals from iron ore. But the high cost of the raw materials and involvement of several steps in preparation of the dispersant prohibits its commercial application. Moreover, phenol is an environmentally harmful chemical. Another poly electrolyte type surface active agent/additive suitable for removal of alumina containing minerals and the like ones from Indian iron ore fines and slimes has been reported in Indian patent No. 175442 (1996). The process uses lignite and sodium hydroxide as the raw materials and involves a few simple steps. The additive is effective in a narrow pH range from 5 to 8. The additive, although is selective to disperse alumina containing minerals and flocculate hematite particles from iron ore fines and slimes but additional stabilizing agent is required for increasing the polyvalent ions compatibility, Humic acid, a giant molecule and one of the main constituent of lignite, having -COOH, phenolic -OH and >C=O groups can be oxidised to increase the functional groups like -COOH by using appropriate oxidising agent. In addition to -COOH, phenolic -OH and >CK) groups, -HSO3 group may also be introduced to the lignite structure by sulfonation using sulphuric acid or the like one as the sulfonating agent under controlled condition. By introducing -HSOs group in the aromatic ring of the humic acid, polyvalent ions compatibility of the additive mav be increased. The main object of the present is to provide a process for the preparation of a surface active agent useful as chemical additive and a polyelectrolyte for the removal of aluminous gangue minerals from ore fines Yet another object is to provide a process for the preparation of a surface active agent which can be used in both acidic and basic medium still another object is to provide a surface active agent which can remove significant amount of alumina containing minerals from low grade iron ores. Accordingly the present invention provides a process for the preparation of a surface active agent useful as chemical additive and a polyelectrolyte for the removal of aluminous gangue minerals from ore fines, which comprises treating lignite as mined or after grinding with dilute sulphuric acid, with lignite to sulphuric acid ratio in the range of 1:5 to 1:10 and heating the resulting mixture, at a temperature of 70-98°C, for a period in the range of 1-4 hrs, followed by filtration or centrifugation of the mixture as such, washing the resultant solid product with water and mixing it with aqueous sodium hydroxide solution and maintaining the solid to sodium hydroxide ratio in the range of 1:0.3 to 1:0.7 and solid to water ratio in the range of 1:5 to 1:10, heating the resultant mixture at a temperature in the range of 60-98°C, for a period of 1-10 hours followed by separation of the liquid product by known methods to obtain the desired product. In an embodiment of the present invention the temperature used for sulfonation of lignite is in the range of 80-90°C. In yet another embodiment the ratio of sulfonated lignite to sodium hydroxide used is 1:0.3 to 1:0.6. In yet another embodiment the surface active agent obtained is effective for the removal of aluminous bearing gangue minerals from ores in both acidic and basic pH. In yet another embodiment the surface active agent obtained is effective for the removal of aluminous bearing gangue minerals from ores in the presence of polyvalent ions. In yet another embodiment the surface active agent obtained is stable at a dose of about 0.05% w/v in aqueous solution containing polyvalent ion (Ca2+) up to 250 ppm. In yet another embodiment the surface active agent obtained gives a stable dispersed phase in slurry of iron ore fines at a dose of 0.02-0.10% w/v. In yet another embodiment the surface active agent obtained gives a stable dispersed phase in slurry of iron ore fines and water at a dose of 0.05-0.08% w/v. In still another embodiment the surface active agent obtained disperses more amount of alumina bearing minerals in ore water slurry beyond two minutes of settling. The present investigation provides a process tor preparing a surface active agent chemical additive/polyelectrolyte effective for removal of alumina bearing minerals from iron ore fines and slimes effective both in acidic and basic pH and even in presence of polyvalent ions using lignite as the major starting material, which consists of treating lignite, as mined or after grinding, with dilute sulphuric acid (50-75%) maintaining lignite to sulfuric acid ratio in the range of 1:5 to 1:10 and heating the resulting mixture at a temperature of 70-98 °C for a period ranging from half an hour to four hours or so followed by filtration or centrifugation of the mixture, washing the solid product with water and mixing it with aqueous sodium hydroxide solution maintaining solid to sodium hydroxide ratio in the range of 1:0.3 to 1:0.7 and solid to water ratio in the range of 1:5 to 1:10, heating the resultant mixture in the temperature range of 60-98 °C for a period of 1 -10 hours followed by separation of the liquid product by filtration, decantation, centrifugation or similar methods. In the embodiment of the present invention, lignite from Neyveli, Tamil Nadu was ground to -150 micron. 50 g of ground lignite was added to dilute sulfuric acid (250 ml) taken i n a three-necked round bottom flask fitted with a stinrer, a condenser and a thermometer maintaining weight of lignite to volume of acid ratio of 1:5. The mixture was slowly heated in the temperature range of 70 to 98 °C and maintained at the temperature for a period of 1 to 4 hours. The mixture was then allowed to cool to room temperature while stirring was continuing. The solid was separated by suitable means like filtration, decantation, centrifugation, washed with water to make acid free and the sulfonated product was then digested with aqueous sodium hydroxide solutions containing 50-70 g sodium hydroxide per 100 g of sulfonated lignite at 60-98 °C for a period of 1-10 hours. The insoluble matters were separated either by settling or by centrifugation. The additive/surface active agent as prepared by the developed process when added in the concentration range of 0.02 to 0.10 %w/v and in the pH range of 3 to 10 to a slurry of lateritic type of iron ore fine-water and iron ore slime-water, produces a stable dispersed phase rich in alumina containing minerals. The iron enriched ore settles down keeping the alumina containing gangue minerals in the dispersed phase due to higher stability of the suspension. The stability of the suspension or the solid content in the dispersed phase was determined by withdrawing fixed volume of the suspension after allowing to settle for different period of time. Finally, the sediment (concentrated iron ore) was collected by decanting the suspension. The invention is illustrated with the following examples which should not be construed to limit the scope of the investigation: Example 1 250 ml of 50% sulfuric acid was taken in a three-necked round bottom flask of 1.0 litre capacity fitted with an electrical stirrer, a thermometer and a condenser. To the dilute sulfuric acid, 50 g of powdered lignite was added in small increment at room temperature with through and continuous stirring. Addition of lignite was completed in about 25 minutes to minimise excess heat generation due to exothermic reaction. The temperature was then increased through an energy regulator to 85±5 °C and maintained at this temperature for four hours. The mixture was allowed to cool to room temperature and filtered. The solid sulfonated lignite was washed with water till it was acid free. The FTER and elemental analysis of typical sulfonated lignite samples are given in Figure 1. 300 ml of water was taken in a three-necked round bottom flask fitted with all accessories for stirring, heating, temperature recording, etc as used above, to which 40 g of sulfonated lignite was added in small increment with continuous stirring. The mixture was digested at 90±S °C for one hour and the temperature was maintained by an energy regulator. 50 ml of 48 % (w/v) NaOH was then added slowly to the mixture in 15 minutes of time and was digested at 90±5 °C for additional four hours with continuous stirring. Additional 150 ml of water was added to the digested product and the mixture was allowed to cool to room temperature. The mixture was transferred to a measuring cylinder of one litre capacity, mixed thoroughly to homogenise and allowed to settle for 12 hours. The surface active agent/additive (supernatant solution) was separated from the sediment by decantation and is termed as SL50. SL50 additive when added in the concentration range of 0.02 to 0.10 % w/v to 10 % w/v slurry of -300 μm iron ore fines gives a stable suspension at pH 8.0. The additive in the concentration range of 0.05 to 0.10 % (w/v) produces a stable dispersed phase containing 1.97 to 2.65 wt% alumina bearing minerals respectively after three minutes settling (Table 1). Example 2 The same experiment as outlined in example 1 was repeated using the same amount of lignite and in the same manner except that the powdered lignite was added to 250 ml of 65% sulfuric as used in example 1 and 40 g of sulfonated lignite was mixed with 300 ml. The resultant mixture was digested at 90±5 °C with sodium hydroxide solution maintaining sulfonated lignite to sodium hydroxide ratio of 1:0.6 for four hours following the same procedure and condition as indicated in example 1. The product was transferred to a measuring cylinder of one litre capacity and the mixture was mixed thoroughly and allowed to settle for 12 hours. The supernatant solution was separated trom the sediment by decantation. The surface-active agent/additive so obtained is termed as SL65. The surface active agent/additive (SL65) as prepared at a dose of 0.02-0.10% w/v produces a very good stable suspension containing 1.94 to 2.53 wt% solid in 10% w/v slurry of-300 μm iron ore fines at pH 8 (table 1). Example 3 Sulfonated lignite sample was prepared by using the same amount of the raw materials and following the same condition and procedure as outlined in example 2 except that the concentration of sulfuric acid which was increased to 75% and alkali digestion of the sulfonated lignite was performed maintaining the same condition and procedure as indicated in example 2. The surface active agent/additive as prepared is termed as SL75. The additive at a dose of 0.02-0.10% w/v and at pH 8.0 also produces a very good stable dispersed phase containing 1.84-2.52 wt% solid in 10 % w/v slurry of -300 um iron ore fines after 3 minutes of settling (table 1). Example 4 Limewater containing variable amount of calcium ion from 50 to 400 ppm was added separately to 100 ml solution containing 0.05% w/v of SL50, SL65 and SL75. The results presented in Table 2 show that all the surface-active agents/additives (SL50, SL65 and SL75) at a dose of 0.05% w/v are compatible up to 250 ppm of calcium ion. Example 5 The dispersibility and the efficacy of the SLSO surface active agent/additive was tested at a dose of 0.02 to 0.08% w/v and at pH 8 for preferential removal of alumina containing minerals and enrichment of iron value in a feed of -10 mm iron ore fines (40% slurry) as mentioned in example 1. The surface active agent/additive at a dose of 0.05% and 0.08% w/v produces a stable dispersed phase with 4.22-4.24% w/v solid after 3 minutes of settling (Table 3). The additive at a dose of 0.05% (w/v) reduces the alumina content of the ore from 2.37 to 1.24% and increases the iron value from 63.25 to 64.57%. Example 6 The dispersibility and efficacy of SL65 surface active agent/additive as prepared in example 2 was tested for alumina removal and iron enrichment at a dose of 0.02-0.08% w/v and at pH 8. It produces a very stable dispersed phase in 40% w/v slurry of -40 mm iron ore fines after 3 minutes of settling with solid content 3.83 to 5.60% w/v (Table 4). The surface active agent/additive at a dose of 0.05% w/v reduces alumina from 2.37% to 1.38% and increases the iron value from 63.25 to 65.44% in the concentrate. The advantages of the present invention are summarised below:- (1) The process makes use of cheap and abundantly available indigenous raw materials (2) The process eliminates the use of concentrated sulfuric acid and handling of which creates problems (3) The additive can be used both in acidic and basic pH of the medium (4) The additive has a very high polyvalent ion compatibility (5) The additive at a very low dose can remove significant amount of alumina containing minerals from low-grade iron ore and bring down its Al2O3 /Fe and Al2O3/S1O2 ratios well below the recommended value for use in iron extraction. Tabte 1 Stability of the suspension of iron ore fines (-300 nm)-water slurry (10% w/v) treated with snrface-active agents/additives at pH8 (Table Removed)Table 2 Calcium ion compatibility of 0.05% solution (w/v) of surface-active agents/additives at different doses of calcium ion (Table Removed)Table 3 Stability of dispersed phase of -10 mm iron ore fines-water slurry (40% w/v) using different doses of SL50 additive at pH 8 and chemical analysis of the concentrate obtained after 3 minutes of settling Stability of the dispersed phase (Table Removed)Table 4 Stability of dispersed phase of -10 ram iron ore fines-water slurry (40% w/v) using different doses of SL65 additive at pH 8 and chemical analysis of the concentrate obtained after 3 minutes of settling Stability of the dispersed phase Chemical analysis of the concentrate (Table Removed) We claim 1. A process for the preparation of a surface active agent useful as chemical additive and a polyelectrolyte for the removal of aluminous gangue minerals from ore fines, which comprises treating lignite as mined or after grinding with dilute sulphuric acid, with lignite to sulphuric acid ratio hi the range of 1:5 to 1:10 and heating the resulting mixture, at a temperature of 70-98°C, for a period in the range of 1-4 hrs, followed by filtration or centrifugation of the mixture as such, washing the resultant solid product with water and mixing it with aqueous sodium hydroxide solution and maintaining the solid to sodium hydroxide ratio in the range of 1:0.3 to 1:0.7 and solid to water ratio in the range of 1:5 to 1:10, heating the resultant mixture at a temperature in the range of 60-98°C, for a period of 1-10 hours followed by separation of the liquid product by known methods to obtain the desired product. 2. A process as claimed in claim 1 wherein the temperature used for sulfonation of lignite is in the range of 80-90°C. 3. A process as claimed in claim 1, wherein the ratio of sulfonated lignite to sodium hydroxide used is 1:0.3 to 1:0.6. 4. A process as claimed in claim 1, wherein the surface active agent obtained is effective for the removal of aluminous bearing gangue minerals from ores in both acidic and basic pH. 5. A process as claimed in claim 1 wherein the surface active agent obtained is effective for the removal of aluminous bearing gangue minerals from ores in the presence of polyvalent ions. 6. A process as claimed in claim 1 wherein the surface active agent obtained is stable at a dose of about 0.05% w/v in aqueous solution containing polyvalent ion (Ca2+) up to 250 ppm. 7. A process as claimed in claim 1 wherein the surface active agent obtained gives a stable dispersed phase containing alumina bearing minerals in slurry of iron ore fines at a dose of 0.02-0.10% w/v. 8. A process as claimed in claim 1 wherein the surface active agent obtained gives a stable dispersed phase containing alumina bearing minerals in slurry of iron ore fines and water at a dose of 0.05-0.08% w/v. 9. A process as claimed in claim 1 wherein the surface active agent obtained disperses more amount of alumina bearing minerals in ore water slurry after two minutes of settling. 10. A process for the preparation of surface active agent useful as chemical additive/polyelectrolyte for the removal of aluminous gangue materials from ores and minerals, substantially as herein described with reference to the examples and drawings accompanying this specification.

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765-del-2006-Abstract-(27-08-2014).pdf

765-del-2006-abstract.pdf

765-del-2006-Claims-(27-08-2014).pdf

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765-del-2006-Correspondence Others-(27-08-2014).pdf

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765-del-2006-Description (Complete)-(27-08-2014).pdf

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765-del-2006-Drawings-(27-08-2014).pdf

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