Reagents for magnetizing nonmagnetic materials

[54] REAGENTS FOR MAGNETIZING NONMAGNETIC MATERIALS

[75] Inventor: Jiann-Yang Hwang, Houghton, Mich.

[73] Assignee: Board of Control of Michigan

Technological University, Houghton,
Mich.

[21] Appl. No.: 167,798

[22] Filed: Mar. 14, 1988

[51] Int. Q.4 C01G 49/08; C04B 35/26

[52] U.S. a 252/62.56; 252/62.51;

427/127

[58] Field of Search 428/403, 692, 900;

427/127; 252/62.51, 62.52, 62.56

[56] References Cited

U.S. PATENT DOCUMENTS

3,926,789 12/1975 Shubert 209/8

4,019,995 4/1977 Briggs 252/62.53

4,094,804 6/1978 Shimoiizaka 252/62.52

4,208,294 6/1980 Khalafalla 252/62.52

4,285,819 8/1981 Yen 210/679

4,356,098 10/1982 Chagnon 252/62.51

Particles of a nonmagnetic material are rendered magnetic by contacting their surfaces with a magnetizing reagent comprising water containing particles of a magnetic material, each of which has a two layer surfactant coating including an inner layer and an outer layer. The inner layer covers the magnetic particle and is a monomolecular layer of a first water soluble, organic, heteropolar surfactant containing at least 3 carbon atoms and having a functional group on one end which bonds with the magnetic particle. The outer layer coats the inner layer and is a monomolecular layer of a second water soluble, organic heteropolar surfactant containing at least three carbon atoms and having a hydrophobic end bonded to the hydrophobic end of the first surfactant and a functional group on the other end capable of bonding with the particles to be magnetized.

13 Claims, 1 Drawing Sheet

REAGENTS FOR MAGNETIZING
NONMAGNETIC MATERIALS

BACKGROUND OF THE INVENTION 5

This invention relates to selectively magnetizing nonmagnetic or paramagnetic particles and to magnetizing reagents useful for that purpose.

Magnetic separation can be an inexpensive, selective and efficient method for separating a particulate mix- 10 ture. Many techniques have been used to magnetize nonmagnetic or paramagnetic particles to permit them to be selectively separated from a mixture by magnetic separation.

For example, U.S. Pat. No. 3,926,789 to Shubert dis- 15 closes wetting the surface of mineral particles with an emulsified magnetic fluid to render them magnetic. C. de Latour, Journal of American Waterworks Association, Vol. 68, p. 443 (1976) discloses using an inorganic coagulant, such as ferric chloride or aluminum sulfate, to 20 agglomerate particles nonselectively in a system which contains a mixture of magnetite and other materials. J. Y. Hwang, et al., IEEE Transactions on Magnetics, Vol. MAG-18, No. 6, p. 1689 (1982) discloses adding an organic polymer flocculant to a mixture of magnetite 25 and other minerals to yield a selective co-flocculation of magnetite and desired minerals.

U.S. Pat. Nos. 4,285,819 to Yen, et al. and U.S. Pat. No. 4,554,088 to Whitehead, et al. disclose methods which involve coating magnetic materials with a poly- 30 mer and then coupling the polymer-coated magnetite particles to the particles to be magnetized. P. Parsonage P, IMM Tenth Annual Commodity, Paper No. fF86007 (1985) discloses introducing fine magnetite into a pulp of mineral slurries in which the desired minerals are 35 conditioned to carry a surface charge opposite to that of magnetite to favor coating of magnetite.

U.S. Pat. Nos. 4,019,995, to Briggs, et al 4,094,804, to Shimoiizaka, 4,208,294, to Khalafalla, et al, 4,356,098 to Chagnon and 4,430,239 to Wyman disclose ferrofluids 40 which are Newtonian liquids containing suspended, small magnetic particles which do not settle out under the influence of gravity and an external magnetic field.

SUMMARY OF THE INVENTION 45

An object of the invention is to provide a magnetizing reagent which is capable of magnetizing a wide variety of particulate, nonmagnetic materials.

Another object of the invention is to provide a method for selectively magnetizing a wide variety of 50 particulate, nonmagnetic materials.

A further object of the invention is to provide a method for separating particulate nonmagnetic materials by magnetic separation.

Other objects, aspects and advantages of the inven- 55 tion will become apparent to those skilled in the art upon reviewing the following detailed description, the drawing and the appended claims.

The invention provides a magnetizing reagent which is capable of magnetizing a wide range of particulate 60 nonmagnetic materials including metallic, nonmetallic, organic and biological materials. The magnetizing reagent comprises water containing particles of a magnetic material, such as magnetite, each of which is coated with a two layer surfactant coating including an inner 65 layer and an outer layer. The inner layer covers the particle and is a monomolecular layer of a first water soluble, organic, heteropolar surfactant containing at

2

least 3 carbon atoms and having a functional group on one end which forms a bond with the magnetic particle and a hydrophobic end. The outer layer coats the inner layer and is a monomolecular layer of a second water soluble, organic, heteropolar surfactant containing at least 3 carbon atoms and having a hydrophobic end bonded to the hydrophobic end of the first surfactant and a functional group oriented outwardly toward the water. Nonmagnetic particles are magnetized by contacting their surfaces with the magnetizing reagent in an aqueous medium and the coated magnetic particles couple with the nonmagnetic particles by adsorption.

"The first and second surfactants can be nonionic, anionic or cationic. The functional group in the second or outer layer surfactant provides the coupling between the magnetic and nonmagnetic particles. Accordingly, the selectiveness of this coupling is controlled by using an outer layer surfactant having the appropriate functional group for the particles to be magnetized and the conditions of the aqueous medium in which the coupling takes place.

Particles of a nonmagnetic material in an aqueous mixture can be separated magnetically by contacting their surfaces with a magnetizing reagent to render them magnetic and then subjecting the mixture to a magnetic separation.

BRIEF DESCRIPTION OF THE DRAWINGS

The single figure is an ideal representation of a magnetizing reagent of the invention in water.

DETAILED DESCRIPTION

The magnetizing reagent of the invention includes a particulate nucleus of a magnetic material. As used herein, the term "magnetic material" means a material having ferromagnetic or strong paramagnetic properties. Suitable magnetic materials include magnetite, ferrites, hematite, maghemite, pyrrhotite and metals, alloys and compounds containing iron, nickel or cobalt. Magnetite is preferred because of its lower cost. The magnetic material may be derived from various sources. For example, magnetite may be obtained from ores and prepared by grinding or by the so-called wet method. Colloidal magnetite can be precipitated by reacting solutions of ferrous and ferric salts with alkali metals in accordance with the procedure described by W. C. Elmore, Physical Review, Series II, Vol. 54, p. 309 (1938). The size of magnetite and ferrite produced by the wet method usually ranges from about 70 angstroms up to 10 or more micrometers.

The particle size of the magnetic material is not particularly critical. Generally, the particle size can range from about 50 angstroms up to 10 micrometers or even higher. Coarser materials have a greater tendency to agglomerate. Such agglomerates can be broken down by a demagnetizing treatment or an ultrasonic dismemberation.

The surfactants, also known as surface active agents, used for the inner and outer layers are substances which exhibit a marked tendency to adsorb at a surface or interface. The surfactants are water soluble or miscible and organic compounds containing 3 or more carbon atoms and having a heteropolar molecule including a functional group or hydrophillic end and a hydrophobic end. Referring to the drawing which is an ideal representation of a magnetizing reagent of the invention in water, the surfactant forming the inner layer is adsorbed 4,834,

3

on the magnetic nucleus with the functional group or hydrophillic end oriented toward the magnetic nucleus and the hydrophobic end pointing radially outwardly. The surfactant forming the outer layer is adsorbed in the opposite direction with the functional group or 5 hydrophillic end oriented toward the water. In actual practice, the hydrophobic ends of the two surfactants may mesh rather than meeting end to end as illustrated in the drawing.

The surfactants used for the inner and outer layers 10 can be various anionic, cationic or nonionic organic surfactants having a hydrophillic functional group and containing 3 or more carbon atoms. The surfactants can be short chain types having a molecular weight as low as about 140 and long chain types containing up to 15 about 120 carbon atoms or more and having a molecular weight up to 20,000 or more. The specific type surfactant used for each layer depends primarily on the nature of the particles to be magnetized with the magnetizing reagent as described in more detail below. This is partic- 20 ularly true for the outer layer surfactant because its functional group is responsible for coupling the magnetic reagent to nonmagnetic particles.

Suitable anionic surfactants include carboxylates, such as caprilic acid, lauric acid, oleic acid and polyoxy- 25 ethylene sorbitan monolaurate; xanthates, such as sodium isopropyl xanthate, sodium isobutyl xanthate, potassium amyl xanthate, potassium hexyl xanthate and potassium nonyl xanthate; dithiophosphates, such as sodium dialkyl dithiophosphate and aryl dithiophos- 30 phoric acid; phosphates, such as polyoxyethylene dinonyphenyl ether phosphate; hydroxamates, such as potassium hexyl hydroxamate and alkyldimethyl ammonium hydroxamate; sulfonates, such as petroleum sulfonate and ammonium lignin sulfonate; sulfonsuccinates, 35 such as sodium dioctyl sulfonsuccinate; taurates, such as sodium-N-methyl-N"coconut oil acid"-taurate; and sulfates, such as sodium cetyl sulfate and sodium lauryl sulfate.

Suitable cationic surfactants include amines, such as 40 hydrogenated-tallowamine acetate, oleyl primary amine acetate, lauric amine, Cs-io oxypropyl amine, trimethylsoy ammonium chloride, 3-aminopropyltrimethoxysilane, primary isodecyl ether amine acetate, coco-amine acetate, tallow-amine acetate and rosin- 45 amine acetate.

Suitable nonionic surfactants include ethers, such as monopentacosane triethyleneglycol ether, monotricosane diethyleneglycol ether, polyoxyethylene-10-oleyl ether, polyoxyethylene-20-oleyl ether, polyoxyethe- 50 lene-4-lauryl ether, polyoxyethelene-10 lauryl ether and polyoxyethelene-23-lauryl ether and alcohols, such as cresol, alpha-(isooctylphenyl)-omega-hydroxypoly (oxy-1,2-ethane-diyl), alpha-triecyl-omegahydroxy-poly (oxy-l,2-ethane-diyl). 55

The inner and outer layers can be formed by any combination of surfactant charge types. That is, the inner and outer layers can be formed by two anionic surfactants, two cationic surfactants, two nonionic surfactants, one nonionic surfactant and one anionic or one 60 cationic surfactant, or one cationic surfactant and one anionic surfactant. Also each layer can be a mixture of surfactants.

The magnetizing reagent can be prepared by first conditioning particles of a magnetic material in water 65 with the surfactant forming the inner layer at a surfactant concentration high enough to provide a monomolecular layer of the inner layer surfactant completely

covering the surfaces of the magnetic particles. As used herein, the term "monomolecular layer" means a single molecular layer of one surfactant or a mixture of surfactant when more than one is used for the inner and/or outer layers.

A suitable acid or base, such as sodium hydroxide or hydrochloric acid, may be added to promote dissolution of the inner layer surfactant. After a monomolecular layer coating of the inner layer surfactant has been obtained, the excess inner layer surfactant is removed from the coated magnetic particles by washing with water or the like. Since the functional group of the inner layer surfactant interacts with the magnetic material, the functional group (hydrophillic end) orients toward the magnetic material and the hydrophobic end points radially outwardly from the magnetic material as illustrated in the drawing.

After removal of the excess inner layer surfactant, the coated magnetic particles are conditioned in water with a sufficient amount of the surfactant for forming the outer layer at a surfactant concentration high enough to provide a monomolecular layer of the outer layer surfactant over the inner layer surfactant and form an aqueous magnitizing reagent. A suitable acid or base may be added to promote dissolution of the outer layer surfactant. Because of a hydrophobic interaction, the outer layer surfactant is adsorbed on the inner layer surfactant with the hydrophobic end attracted toward the inner layer surfactant and the functional group (hydrophillic end) pointing radially outwardly toward the water as illustrated in the drawing.

Difficulties may be encountered when attempting to coat an anionic inner layer surfactant with a cationic outer layer surfactant, and vice versa, because of the opposite charges. This difficulty can be alleviated by washing the single coated magnetic material with a suitable polar solvent, such as ethanol, after removal of the excess inner layer surfactant. When larger particles of magnetic materials are used as the nucleus, it may be necessary to subject the resulting magnetizing reagent to a demagnetizing or ultrasonic treatment as mentioned above.

The following examples are presented to exemplify preparation of magnetizing reagents of the invention from a variety of surfactants and should not be considered as limitations to the invention.

EXAMPLE 1

Colloidal magnetite was prepared by the wet method. 3.4 g FeS04»7H20 and 4.8 g FeCl3»6H20 were dissolved in 10 ml water and 10 ml of concentrated ammonia solution (56%) was added with rapid mixing to yield magnetite precipitates. The solution was heated to boiling (about 90° C.) and the average size of the precipitated magnetite particles increased from about 70 to about 90 angstroms. The magnetite particles were collected on a magnet, washed with water to remove the residual salts and a yield of about 2.2 g of magnetite particles was obtained.

EXAMPLE 2

0.8 g of lauric acid was added to an aqueous slurry the colloidal magnetite prepared in Example 1 (2.2 g colloidal magnetite in 10 ml water) and 5 drops of a 10 N sodium hydroxide solution were added to improve the dissolution of lauric acid. The slurry was heated at 80° C. for 30 minutes to aid the adsorption of lauric acid onto the magnetite. Hydrochloric acid was then added