Solid-solid separations utilizing alkanol amines

Abstract: The separation of silica or siliceous gangue from one or more desired minerals in an aqueous slurry via mechanic means is improved by the addition of a small amount of an alkanol amine to the slurry. Examples of separation techniques benefiting from this technology include using cyclones, tables and spiral separators.

Description: This invention relates to the selective separation of certain solids from solid mixtures containing silica or siliceous gangue. The processing of mixed solids in particulate form is widely practiced in industry. The solids are usually separated into individual components (solid/solid separation) by a variety of engineering processes using inherent differences between the various solid components. These inherent differences include color, size, conductivity, reflectance, density, magnetic permeability, electrical conductivity and surface wettability. This latter characteristic, surface wettability, is exploited in froth flotation, flocculation and agglomeration processes which rely heavily on various chemical treatments to enhance separation. Differences in the other characteristics identified above, especially size, conductivity, density, magnetic permeability and electrical conductivity, have typically been utilized to obtain separation via various mechanical methods. These methods include the use of screening, wet cyclones, hydroseparators, centrifuges, heavy media devices, desliming vessels, jigs, wet tables, spirals, magnetic separators and electrostatic separators. The proper use of water is recognized as critical to the efficiency of such methods. A fundamental driving force in most of these operations is the control of how particles flow, settle or are magnetically or electrically manipulated in an aqueous environment. Factors such as the density (percent solids by weight) of the solid mixture solutions in water; the degree of mechanical agitation of such pulps; the size of particles in the solid mixtures; and the equipment design and size all act and/or are controlled in a complex fashion to optimize the appropriate solid separation in any specific operation. While some universal scientific and engineering concepts can be applied in such separations, the complexity of such operations frequently requires empirical testing and adjustment to effect a suitable separation. The present invention is a solid/solid separation process wherein an aqueous slurry of solids containing silica or siliceous gangue and one or more minerals is mechanically separated, characterized by the addition of an amount of an alkanol amine to the aqueous slurry effective to modify the interaction of the silica or siliceous gangue with the aqueous medium such that separation of the silica or siliceous gangue from the remainder of the solid minerals is enhanced when compared to processes conducted in the absence of the alkanol amine. Mechanical separation refers to those methods in which an aqueous slurry of solid particles is separated based on the physical characteristics of the particles. Such physical characteristics include size, conductivity, density, magnetic permeability and electrical conductivity. Typical means used to separate solid/solid pulps include jigs, wet tables, spirals, heavy media devices, screening, wet cyclones, hydroseparators, centrifuges, desliming vessels, magnetic separators and electrostatic separators. These techniques are well known in the art and are extensively practiced. A general discussion of these techniques is found in Perry's Chemical Engineers' Handbook, Sixth Edition, edited by Don W. Green, McGraw-Hill Book Company. The typical manner of practicing these methods of mechanical separation is not modified by the practice of this invention, other than by the addition of the alkanol amine. Typically, mechanical separation is used to separate particulate solids with sizes ranging from about 100 millimeters (mm) in diameter down to particles of less than 0.001 mm in diameter. Particles of this size range may be obtained in various ways, but are typically obtained by wet grinding. Once ground, the particles are present in an aqueous slurry ranging from 2 to 70 percent by weight solids depending on various factors such as the particular method of solid separation used and other related operating conditions. The alkanol amines of the present invention preferably correspond to the formula NR 1 R 2 R 3 wherein R 1 is a C 1 -C 6 hydroxy alkyl moiety and R 2 and R 3 are individually in each occurrence hydrogen or a C 1 -C 6 hydroxy alkyl moiety. Preferred alkanol amines are monoethanolamine, diethanolamine, triethanolamine, isopropanolamine, hexanolamine and mixtures thereof. The most preferred alkanolamine is diethanolamine. It will be recognized by those skilled in the art that commercial methods of production of such compounds as diethanolamine result in a product containing some by-products such as other alkanol amines. Such commercial products are operable in the practice of the present invention. It will also be recognized that the alkanol amines are themselves compounds and do not form a part of a larger molecule. The amount of such alkanol amines used in the process of this invention is that which is effective to result in increased recovery of the desired solid either through improved grade, improved recovery or a combination thereof. This amount typically ranges from 0.01 to 10 kilogram of alkanol amine per metric ton of dry feed. Preferably, the amount ranges from 0.05 to 1 kg per metric ton and more preferably from 0.1 to 0.5 kg per metric ton. The alkanol amine is added to the aqueous slurry feed prior to the feed being fed to the separation device. It is preferred that, when the solid feed is subjected to grinding that the alkanol amine be added to the grinding step. Example 1 -- Magnetic Separation A continuous 12 inch (30 cm) diameter by 7 inch (18 cm) width wet drum magnetic separator (ERIEZ Laboratory Model 500-11-11) is set up to run at twenty-five percent of maximum intensity using 115 volts and 5.2 amp input. Several batches of feed material were prepared using a mixture of magnetite with a specific gravity of 3.96 and silica with a specific gravity of 2.67. The feed mixture of particles was 15.5 weight percent magnetite. The feed mixtures were prepared in aqueous slurry form at 20 weight percent solids in a special highly agitated slurry holding tank that provided a uniform feed slurry to the magnetic separator. In one run, no pre-treatment was used and in the second run, the slurry was treated with diethanolamine in an amount equivalent to 0.45 kg per metric ton of dry feed solids. Each run was operated at steady state conditions and samples were collected from the concentrate, overflow and tail for five minutes. The samples were dried, weighed and an iron analysis done with a D.C. plasma spectrometer to determine that fate of the magnetite. The results obtained are shown in Table I below. The data above shows that the addition of diethanolamine results in more iron being recovered in the concentrate and less iron lost in the tailings. Example 2 A 0.6 x 1.3 m laboratory table separator was used with 0.01 m openings between the ribs which measured 0.003 by 0.0017 m. The table angle was 10 degrees from horizontal with moderate agitation and water washing. The feed material used was 15.5 weight percent magnetite with the remainder silica. The same slurry feeding system was used and all table operating conditions and slurry feed rates were held constant in each run. Two steady state runs were made at 20 weight percent solids in an aqueous slurry. Sampling of product, middlings and tail were made for seven minutes in each run. All samples were dried, weighed and analyzed for iron using a D.C. plasma spectrometer. The definition of samples with this table is defined by the physical placement of overflow trays. The results obtained are shown in Table II below. The data above shows a significant increase in the amount of iron recovered. The primary effect appears to be in the shift of iron from the middlings to the product. Example 3 Samples of specified ores (300 g each) were ground in an eight inch (20 cm) diameter ball mill using one inch (2.5 cm) diameter stainless steel balls to obtain approximately 50 weight percent less than 37 micrometers in diameter. The mill was rotated at 60 revolutions per minute (RPM) and 600 cm 3 of water was added along with any desired chemical to the mill before grinding was initiated. When the target grind size is achieved, the mill contents were transferred to a 10 liter vessel and the contents were diluted with water to make up a total pulp volume of 10 liters. The dilute pulp was mixed for one minutes at 1800 RPM and then settling was allowed to occur for five minutes. Then seven liters of the pulp from the upper zone of the vessel were decanted. The dry weights of both the decanted solids and the settled solids were recorded and the weight percent in the deslimed fraction was calculated. The higher this deslime weight fraction, the more efficient the desliming or fine particle removal process. The three ores chosen were an iron ore containing 32 weight percent silica; a copper ore containing 76 weight percent silica and siliceous gangue and a phosphate ore containing 44 weight percent silica and siliceous gangue. The identity and dosage of the alkanol amines used is shown in Table III below. The data in Table III shows that various alkanol amines are effective in increasing the percentage of very fine particles removed in a desliming process. As in this example, the very fine (high surface area) particles present in many finely ground mineral samples are rich in undesired silica and/or siliceous gangue. Their removal is important in subsequent treatment steps involving the addition of chemical reagents such as in flotation. Example 4 A standard five turn Humphrey spiral was set up with constant feed pulp and feed water capability. Only one concentrate port was used (remainder were sealed off with smooth discs) to obtain consistent steady-state conditions. Sufficient wash water was supplied to maintain a reasonably smooth flow pattern over the concentrate port which was located at the bottom of the first spiral turn. Each run described in Table IV below consists of a five-minute sampling period with the feed rate being 3.0 kg of a 20 weight percent solid slurry over the five minute period. Four different ores were used: (1) cassiterite (SnO 2 ) containing 0.65 weight percent tin with 1.2 weight percent larger than 10 mesh (2mm.) and 9.9 weight percent smaller than 200 mesh (75µm); (2) coarse hematite (FeO 3 ) containing 33.1 weight percent iron with 8.6 weight percent being larger than 10 mesh (2mm) and 2.1 weight percent being smaller than 200 mesh (75µm); (3) fine hematite containing 47.4 weight percent iron with 0.0 weight percent being larger than 10 mesh (2mm) and 28.3 weight percent being smaller than 200 mesh (75µm); and (4) coarse rutile (TiO 2 ) containing 8.8 weight percent iron with 11.4 weight percent being larger than 10 mesh (2mm) and 4.9 weight percent being smaller than 200 mesh (75µm). In each run, all samples were collected, dried and weighed and metal content determined by a D. C. plasma spectrograph. When the diethanolamine was used, the feed slurry was conditioned for one minute in a stirred tank before slurry feed addition to the spiral was initiated. The results obtained are shown in Table IV below. Ore Wt % Ore Recovered Grade of Recovered Ore % of Metal Recovered No DEA DEA No DEA DEA No DEA DEA SnO 2 Concentrate 34.1 39.6 1.34 1.32 70.3 80.4 Tail 65.9 60.4 0.29 0.21 29.4 19.5 Coarse Fe 2 O 3 Concentrate 38.0 35.4 38.1 45.0 43.7 48.1 Tail 62.0 64.6 30.1 26.5 56.4 51.7 Fine Fe 2 O 3 Concentrate 50.3 56.8 53.7 53.1 57.0 63.6 Tails 49.7 43.2 41.0 40.0 43.0 36.4 Rutile Concentrate 11.0 10.1 41.7 50.1 52.125 57.5 Tails 89.0 89.9 4.7 4.2 47.5 42.9 The data above shows that, in each case, the overall recovery of the desired metal is increased by the practice of the present invention. Example 5 -- Hydrocyclone Separation A one inch (2.5 cm) hydrocyclone unit having a constant feed slurry pumping device was used. Steady state feed conditions and a uniform discharge fan were established prior to sampling the underflow and overflow discharge. The feed slurry of hematite ore contained 34.6 weight percent SiO 2 and was about 6 weight percent solids. When used, the alkanol amine was added to the slurry feed box which was highly agitated to ensure uniform feed to the cyclone. Samples were sized on standard screens to detect any shift in separation efficiency. The results obtained are shown in Table V below. Example 6 -- Hydrocyclone Separation The process described in Example 5 was used with the exception that the ore used was a phosphate ore containing 58.1 weight percent SiO 2 . The results obtained are shown in Table VI below. The data in Tables V and VI show that the use of the alkanol amines increases the amount of silica containing fines removed from the two ores tested. It is also clear that while the weight percent of material included in the coarse underflow decreases slightly, the percentage of that material which is of the desired larger particle size increases. Example 7 -- Viscosity Effects on Silica Slurries An aqueous silica slurry containing 60 weight percent solids and 82.4 weight percent less than 75 µm was prepared. The samples were well mixed and then viscosity was measured using a Brookfield RVT viscometer with a T-bar and helipath stand. The samples were allowed to stand undisturbed for 24 hours after viscosity measurements are taken and then the height of the solid rich lower zone was measured. The data obtained is shown in Table VII below. Alkanolamine Dosage kg/metric ton Viscosity (cps x 100) Height of Solid Zone (cm) None --- 46 8.9 Diethanolamine 0.45 50 11.3 0.90 55 13.7 2.00 62 15.4 Monoethanolamine 0.45 49 10.5 Isopropanolamine 0.45 48 10.1 Hexanolamine 0.45 47 9.6 Triethanolamine 0.45 47 9.3 The data in Table VII shows that the alkanol amines of the present invention have a general effect on the viscosity of aqueous silica slurries and on the rate or degree of settling of the silica particles when left undisturbed. The alkanol amine appears to keep the fined silica particles in suspension to a greater degree.

Claims: A solid/solid separation process wherein an aqueous slurry of solids containing silica or siliceous gangue and one or more minerals is mechanically separated, characterized by the addition of a (C 1 -C 6 alkanol) amine to the aqueous slurry in an amount effective to modify the interaction of the silica or siliceous gangue with the aqueous medium such that the separation of the silica or siliceous gangue from the remainder of the solid minerals is enhanced. A process as claimed in Claim 1 wherein the alkanolamine corresponds to the formula NR 1 R 2 R 3 wherein R 1 is a C 1 -C 6 hydroxy alkyl moiety and R 2 , and R 3 are individually in each occurrence hydrogen or a C 1 -C 6 hydroxy alkyl moiety. A process as claimed in Claim 2, wherein the alkanol amine is selected from monoethanolamine, diethanolamine, triethanolamine, isopropanolamine, hexanolamine and mixtures thereof. A process as claimed in Claim 3, wherein the alkanol amine is selected from diethanolamine, monoethanolamine and mixtures thereof. A process as claimed in Claim 4, wherein the alkanol amine is diethanolamine. A process as claimed in any one of the preceding claims, wherein the solids contained in the aqueous slurry are subjected to a grinding step prior to being mechanically separated and the alkanol amine is added to the grinding step. A process as claimed in any one of the preceding claims, wherein the alkanolamine is used in an amount of from 0.01 to 10 kilograms of alkanolamine per metric ton of dry feed. A process as claimed in Claim 7, wherein said amount is 0.05 to 1 kg/metric ton. A process as claimed in Claim 8, wherein said amount is 0.1 to 0.5 kg/metric ton. A process as claimed in any one of Claims 1 to 9, wherein the solid/solid separation process uses wet tables. A process as claimed in any one of Claims 1 to 9, wherein the solid/solid separation process uses desliming vessels. A process as claimed in any one of Claims 1 to 9, wherein the solid/solid separation process uses hydroseparators. The use of a (C 1 -C 6 alkanol) amine to enhance mechanical separation of silica or siliceous gangue from one or more minerals admixed therewith in a slurry. A use as claimed in Claim 13, wherein the alkanol amine is as defined in any one of Claims 2 to 5 or is used in an amount as defined in any one of Claims 7 to 9.

Inventors: FEE BASIL S, KLIMPEL RICHARD R, LEONARD DONALD E, FEE, BASIL S., KLIMPEL, RICHARD R., LEONARD, DONALD E.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1992
Main classification: B03B1
IPC codes: B03B1, B03B5