US3657997A

US3657997A - Recovering metal values

Info

Publication number: US3657997A
Application number: US800108A
Authority: US
Inventors: Vincent A Vellella
Original assignee: Pittsburgh Pacific Processing Co
Current assignee: Pittsburgh Pacific Processing Co
Priority date: 1969-02-18
Filing date: 1969-02-18
Publication date: 1972-04-25
Anticipated expiration: 1989-04-25

Abstract

Materials containing metal values and contaminants are subjected to a grinding operation to selectively pulverize the contaminants while minimizing grinding action on the metal values. Selective grinding is effected by controlling power input to the grinding operation. The material is ground as a pulp, and pulp density is controlled for continuous operation of the grinding mill. Pulverized contaminants are hydraulically separated from metal values in turbulators operated in parallel-flow arrangement to permit continuous discharge from the grinding mill. Underflow from turbulators passes into a rake classifier. Underflow from the classifier is dried in a hot gas blast, where separation of piggyback slimes is effected. Dried concentrate is briquetted. In a preferred embodiment, residues from grinding stainless steels are subjected to selective grinding to break away grinding wheel components bonded to the metal particles and to pulverize grinding wheel components and other contaminants while minimizing work hardening of the metal particles to avoid impairment of the ability of the metal particles to be briquetted.

Description

United States Patent Vellella 1541 'RECOVERING METAL VALUES 1 [72] Inventor:

vmm .4. Vellella, Cleveland, 01115 [73] Assignee: Pittsburgh Pacific Processing Co. 1221 Filed: 55114121959 21; Appl.No.: 300,105

1521 u.s.c1. ..1oo/39,241/14,241/21, 241/30 51 men... "133011 l3/00,B02cl7/04,B02c2l/00 531 FieldoISearch ..241/14,11,2o,21,30,32, 241/o1o. 22, 24; 209/12, 153; 100194-93, 90, 91, 39

551 Relereneee c1151:

umrso s r/mas PATENTS 1,999,325 4/1935 53111511151111 ..241/14 2,023,313 1/1935 3155111551133. .241/14x 2,251,325 9/1941 "Black.......... ..241/14 2,302,535 11/1942 Weber..... 241/2ox 2,441,534 5/1943 315195111... ..241/20 2,154,051 1/1955 Klugh 241/21x 3,013,912 1/1952 Steinmetz 241/3211 3,049,053 3/1952 Rath ..241/14 3,031,954 3/1953 1155115113,- ..241/14 115] 33,657,997 [451 Apr. 25, 1972 Primary Examiner- Donald G. Kelly Attorney-Shanley and O'Neil 1 l 5 7} ABSTRACT Materials containing metal values and contaminants are subjected to a grinding operation to selectively pulverize the contaminants while minimizing grinding action on the metal values. Selective grinding is effected by controlling power input to the grinding operation. The material is ground as a pulp, and pulp density is controlled for continuous operation of the grinding mill. Pulverized contaminants are hydraulically separated from metal values in turbulators operated in parallel-flow arrangement to permit continuous discharge from the grinding mill. Underflow from turbulators passes into a rake classifierf'Underflow from the classifier is dried in abut gas blast, where separation of piggyback slimes is effected. Dried concentrate is briquetted. In a preferred embodiment,

residues from grindingstainl ess steels are subjected to selective grinding to break away grinding wheel components bonded to the metal 155111515 and to pulverize grinding wheel components and other contaminants while minimizing work hardening of the metal particles to, avoid impairment of the ability of the metal particles to be briquetted.

26 Claims, 6 Drawing Figires UlllERFLOI 4o WERFLO' UNDERFLOW 58 BRDUETTIIG PRE mooucr Ill PATENTEDAPR 25 1972 3,657, 99 7 SHEET 1 or 3 WATER 34 4s TURBULATOR TURBULATOR 3a OVERFLOW T UNDERFLOW RAKE CLASSIFIERI 42 OVERFLOW r UNDERFLOW 5o RAKE CLASSIFIER 52 I 54\ DEWATER DENSIFIER ,ovemow UNDERFLOW Y DRYER RECLAIM RECLAIM 5e\ BRIOUETTING PRESS PRODUCT /|4s 4 vmcmr A; VELLELLA F|G.5 BY M ATTORNEY;

RECOVERING METAL VALUES BACKGROUND OF THE INVENTION Residues produced by grinding metal objects contain much valuable metal in the form of metal particles. For example, many tons of residues are produced in the steel industry by the grinding of slabs and like objects of stainless and other alloy steels for purposes of surface preparation. The alloy steel particles are valuable chiefly for their content of expensive alloying elements, e.g. chromium.

However, as a result of the grinding operation, the residues contain many nonmetallic contaminants. The contaminants include grindingwheel components intimately mixed with the metal particles. Many of the contaminants are tightly bonded to the metal particles by mechanical and other forces applied in the grinding operation.

The grinding wheel components include grinding wheel binders and/or their decomposition products. Such materials commonly contain sulfur. Other grinding wheel components which contaminate the grinding residues are grits of abrasive material, e.g. silicon carbide and alumina. The contaminants make alloy steel grinding residues unsuitable for use as steelmaking furnace charge without performance of a reclamation procedure in which the bulk of the contaminants is removed.

Various reclamation procedures have been proposed for recovering metal values from grinding residues. However, the treatments proposed heretofore have had some disadvantage or deficiency which prevented their being entirely satisfactory. Some do not effect sufficient separation of the contaminants, particularly as regards the contaminants adhered to the metal particles. Others require a melting operation, which is expensive and leads to loss of expensive alloying elements from the metal.

Accordingly, a main object of the invention is provision of an improved system for recovering. metal values from intermixture with contaminants.

Other objects and advantages of the invention will appear from the following detailed description which, together with the accompanying drawings, discloses a preferred embodiment of the invention for purposes of illustration. only. For definition of the invention, reference will be made to the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, where similar reference characters denote similar elements throughout the several views:

FIG. 1' is a flow sheet schematically illustratinga reclamation system embodying principles of the invention;

FIG. 2 is a side cross-sectional view schematically illustrating details of apparatus employed in the systemof FIG. 1;

FIG. 3 is a plan view of the structure of FIG. 2;

FIG. 4 is a view of details of the structure of FIG. 2;

FIG. 5 is a cross-sectional view schematically illustrating details of drying apparatus employedin the system of FIG. 1; and

FIG. 6 is a cross-sectional view on line 6-6 of FIG. 5;

DESCRIPTION OF THE PREFERRED EMBODIMENT Grinding residues containing stainless steel particles and grinding wheel components are received in a feed bin 10 (FIG. 1). The metal particles are closely intertwined, resembling steel wool having giant fibers. The grinding wheel components are present as particles of abrasive and of sulfur-containing wheel binder, bonded to the metal particles and otherwise in admixture therewith. The abrasive materials include silicon carbide and alumina. The grinding residues also contain contaminating particles of oxides of ironand chromium, chiefly from scale present on the steel during the grinding operation which produced the residues. Many of the metal particles are believed to be at least partially. coated with an ultrathin sulfurcontaining film of grinding wheel binder and/or decompositionproducts thereof.

The residues are transferred from bin 10 to a screen 12 for removal of lumps. Undersize from screen 12 is passed with water from a source 14 into a rod mill 16 where the residues are subjected to grinding by contact with grinding rods 18 (FIG. 2). Rod mill 16 is conventional, including a cylindrical body 20 and opposed trunnions 22, 24 which are mounted for rotation in supports (not shown). Screened grinding residues are received in a hopper 26 and passed downwardly through a conduit 28 which includes an elbow 30 and extends into trunnion 22 to discharge grinding residues into rod mill 16. A water conduit 32 passes through the walls of conduit 28 at elbow 30 and injects a stream of water along conduit 28 into rod mill 16 to aid passage of the fibrous residues into the mill. The water and grinding residues form a pulp in which the grinding residues are subjected to the grinding operation. Water flow rate is controlled by a conventional flow meter 33.

The grinding operation is controlled to effect a selective grinding in which the nonmetallic contaminants adhering to the metal particles are broken away and pulverized along with nonadhering contaminants, while grinding action on the metal particles is minimized to avoid work hardening of the metal particles to an extent which would impair the ability of the metal particles to be briquetted without a separate binding material and without performance of an annealing operation. It is necessary to briquette recovered metal particles before use as steelmaking furnace charge, to facilitate handling, pro vide sufficient mass for the particles to sink below the melt surface and otherwise provide improved melting characteristics.

Difficulties encountered in a briquetting operation become increasingly worse with an increasing amount of work hardening. of the particles being briquetted. In briquetting without a separate binding material, the particles are cohered as a briquette by flow of metal of the particles. The metal flow effects bonds among the particles. When the particles are excessively work hardened, little or no metal flow occurs to bind the particles together, and the briquettes have poor cohesion and fall apart. Also, as the degree of work hardening increases, the resistance of the particles to being packed together increases and the spaces between particles remains larger, so that the briquettes are of lower density. Finally, when the particles are excessively work hardened, the force required for effective compaction may exceed that which can be applied by the briquetting press.

When briquetting becomes too difficult because of excessive work hardening of the metal particles, it is necessary to anneal the metal particles or employ a separating binding agenLAnnealing softens the metal particles, but is a cumbersome procedure and is complicated by necessity for provision of a controlled atmosphere to prevent. oxidation of the particles. It is preferred to perform the briquetting operation in absence of a separate binding material, because binders complicate the briquetting operation and involve additional costs. Necessity for annealing or use of a special briquette binding material is avoided in accordance with the invention by controlling the grinding operation to break away and selectively pulverize the nonmetallic contaminants while minimizing work hardening of the metal particles from contact by grinding rods, so that no difficulties arise in briquetting the recovered metal particles.

The desired selective grinding action is effected by controlling power input to the grinding mill. The power input to the mill is established at a magnitude within a range having a minimum defined by the amount of rod mill work energy necessary to effect a satisfactory degree of breaking away and pulverization of contaminants, and a maximum defined by the amount of work hardening which can be effected on the particles without presenting briquetting difficulties. The operable range will vary for the type of metal being processed, because some metals are more easily work hardened than others. For steel grinding residues, maintaining the power input to the grinding operation at a value of about 20 to 40 kilowatt hours per ton of grinding residues, preferably about 30 kilowatt hours per ton, effects the desired selective grinding.

The grinding operation is continuous, i.e., performed with continuous feed of pulp components (grinding residues and water) into mill 16 through trunnion 22, and continuous overflow discharge of ground pulp from trunnion 24. In order to effect satisfactory continuous operation, the pulp density, i.e., percent solids, is controlled within a range having a minimum defined by quantitative production requirements and a maximum defined by difficulties which prevent satisfactory continuous operation. It has been found that the maximum is substantially less than recommended by conventional teachings for efficient rod mill operation.

The prior art recommends that rod mills be operated at a pulp density of at least 65 percent solids by weight. However, it has been found that when pulp density exceeds about 60 percent solids by weight, one or more of the following adverse results are produced: (1) the grinding rods tend to float out of the mill; (2) the pulp solids tend to stay in the mill and only the water discharges; (3) grinding action of the rods is reduced by solids packed in interstices between the rods. To avoid these results while obtaining maximum throughput, it is preferred to establish pulp density within a range of about 45 to 55 percent solids by weight. Most preferably, the pulp density is controlled at 50 weight percent solids. Control of pulp density is effected by varying the rate of feed of grinding residues to the mill, and/or varying the rate of flow of injected Water. Unless otherwise specified, all composition percentages herein are by weight.

Returning to FIG. 1, discharge from rod mill 16 is passed to one of a pair of alternately operating turbulators 34, 36 which are in parallel-flow relationship with one another. The turbulators separate relatively light, pulverized nonmetallic contaminants from relatively heavy metal particles by hydraulic classification. The bulk of the metal particles emerges from the turbulators in an underflow 38, which is discharged into a rake classifier 40 for further concentration producing an underflow 42 and an overflow 44.

The bulk of the nonmetallic contaminants emerges from the turbulators in an overflow 46 which is passed into another rake classifier 48. Overflow 44 from rake classifier 40 is also passed into classifier 48, which produces an overflow 50. Overflow 50 is rich in nickel and, if desired, suitable reclamation procedures can be effected for recovery thereof. The underflow 52 from rake classifier 48 contains the bulk of the abrasives and some of the smaller metal particles and, if desired, suitable reclamation procedures can be effected on underflow 52 for recovery of valuables contained therein.

Underflow 42 from rake classifier 40 contains the bulk of the metal particles. Underflow 42 is dewatered in classifier 40 and, if desired, can be further dewatered in a dewater densifier 54, which can be of any suitable type of conventional design. The dewatered material is then passed to a dryer 56, which dries the metal particles and dries and breaks away and separates piggyback slimes therefrom. The dried particles are then passed to a briquetting press 58 and the briquettes to a product bin 60.

Rod mill 16 continuously discharges into a trough 62 (FIGS. 2,3) which extends transversely across the deep end of rake classifier 40. Rake classifier 40 is disposed in side-by-side relationship with rake classifier 48. The rake classifiers are separated by a common division wall 63 and respectively include

large bodies

66, 68 of aqueous liquid (see also FIG. 4). Wall 63 includes a lower portion 64 which acts as a weir for overflow of liquid from liquid body 66 to liquid body 68.

Pulp in trough 62 flows through openings in the trough bottom wall into conduits 70, 72. The bottom wall slopes downwardly in opposite directions toward the conduits. A small stream of water is supplied by a conduit 65 to the bottom portion of trough 62 at each conduit, to prevent stagnant flow conditions from developing in the trough. The top portions of conduits 70, 72 are respectively provided with

valves

74, 75 for opening or closing of the conduits to flow of pulp. Conduits 70, 72 supply pulp to

hydroclassification turbulators

34, 36, respectively. The turbulators are identical, so description of one will impart an understanding of both. Primed reference numerals on turbulator 36 indicate elements corresponding to unprimed numerals on turbulator 34.

Turbulator 34 includes an upstanding tubular member 76 having sidewalls 77 defining an upwardly extending classification passageway 78. Tubular member 76 includes a cylindrical upper portion in the form of a tube 80, and a cylindrical lower portion 82 having a larger diameter than tube 80. Enlarged portion 82 receives the lower end portion of tube 80, defining an annular area 81 surrounding the lower end of the tube. An overflow discharge opening 83 is formed at the top end of tube for overflow of liquid from passageway 78.

The walls of cylindrical lower portion 82 of tubular member 76 define a concentrate storage area 84, and include a frustoconical bottom portion 85 which slopes downwardly to a circular discharge opening 86. Discharge opening 86 is opened and closed respectively by downward and upward movement of a conical bell 88. Movement of bell 88 to selectively open and close opening 86 is effected through a bell rod 89. Bell rod 89 extends axially through passageway 78 upwardly to a lifting and lowering device 91, which can be of any suitable type and is disposed above overflow discharge opening 83.

A water input conduit 90 communicates with passage 78 through an opening in the walls of enlarged portion 82. Water tangentially enters passageway 78 at annular area 81, passes under the lower end of tube 80 and upwardly in the tube. Pulp feed conduit 70 communicates with passageway 78 through an opening in the sidewalls of tube 80, at a location above water input conduit 90. A collecting pan 92 surrounds overflow opening 83 for collecting overflow from passageway 78. Collected overflow is drained through a conduit 94 and passed into a header 96 for transfer to rake classifier 48.

When bell 88 is seated on discharge opening 86, after a brief period for filling of passageway 78 to the level of water input conduit 90, water supplied through conduit 90 can flow in no other direction but upwardly in passageway 78, so an upwardly flowing stream of water is established in the passageway. Pulp entering through conduit 70 is ejected laterally into the rising stream of water, and upon entry into the rising stream, hydraulic classification of the ground materials is initiated. The finely pulverized, nonmetallic contaminant particles which are light in relation to the metal particles are carried upwardly by the rising current to overflow opening 83 and discharged as overflow. Thus, separation of contaminating grinding wheel components and iron and chromium oxides from the metal particles is effected, chiefly by elutriation. Because of high pulp density on entry from conduit 70, it is believed that some classification by hindered settling is effected upon entry of the pulp into passageway 78, and that such classification is followed by classification by free settling as the particles pass downwardly in passageway 78 and disperse.

The metal particles pass downwardly through the rising liquid stream and collect in the lower end portion of passageway 78 defined by storage area 84. The metal particles collect until discharged into rake classifier 40 by lowering bell 88.

Turbulators

34, 36 are arranged in parallel-flow relationship to permit continuous operation of grinding mill 16 yet provide adequate residence time in the turbulators for effective separation. The operation is as follows: Rod mill 1 6 continuously discharges into trough 62. Valve 74 is opened and valve 75 is closed. Bell 88 in turbulator 34 closes discharge opening 86, and water from input conduit 90 fills passageway 78 to overflowing. Pulp flows through conduit 70 into the rising liquid stream in passageway 78, and separation of pulverized contaminants from metal particles is effected, with the metal particles passing downwardly in passageway 78 and collecting in storage area 84. At the end of a predetermined time, governed by storage capacity of the turbulator, valve 74 is closed. Valve 75 is opened with the discharge opening in turbulator 36 being closed and water supplied by conduit 90 filling turbulator 36 to overflowing. Opening of valve 75 to supply pulp from trough 62 to turbulator 36 initiates hydraulic classification of pulp in turbulator 36, while the last pulp input to turbulator 34 is classified and the metal particles settle down through passageway 78. When sufficient time has elapsed for such settlement, bell 88 is moved downwardly and metal particles collected in storage area 84 are dumped into rake classifier 40. When turbulator 34 is emptied of metal particles, the bell is raised to close opening 86 and water supplied through conduit 90 again fills passageway 78 to overflowing for again receiving pulp discharge. When turbulator 36 is charged to capacity, valve 74 is opened for turbulator 34 to repeat its separation cycle. Valve 75 is closed so that supply of pulp to turbulator 36 is terminated and the settlement, dumping and refilling portions of its cycle can be effected while turbulator 34 is working.

The rising current velocity in the turbulators which is necessary to effect the desired separation will vary with the mass and shape of the particulate material being processed. For the steel grinding residues, rising current velocities of about to 35 feet per minute, preferably about feet per minute, effect adequate separation.

Metal particles are discharged from both turbulators at a location spacedabove the bottom of classifier 40. The metal particles settle to the bottom of the classifier, undergoing desliming as they settle. Water in the classifier rises gently as it is displaced by settling metal particles, but the liquid body 66 is quiescent relative to the liquid in the classifying passageways in the turbulators. Slime-laden water overflows from classifier 40 across weir 64 from the top portion of liquid body 66. Discharge opening 86, storage chamber 84, and the lower portion of tube 80 are located below the level of weir 64, so that turbulator 34 is partly submerged in liquid body 66. Turbulator 36 is similarly disposed. The closed bottom turbulators permit such partial submergence which contributes to a vertically compact arrangement. However, if desired, the turbulators can be located at a level above liquid body 66, entirely out of the water.

Metal particles settled to the bottom portion of classifier 40 are raked upwardly along a slanting bottom wall 98 of the classifier. This is effected by a reciprocating rake 99 having a plurality of parallel paddles 100 secured to an operating bar 102. The paddles are spaced axially along the bar, which is operated by a conventional drive mechanism (not shown) to move in a closed path illustrated by arrow 104. In moving along the path, rake 99 is moved upwardly along wall 98 dragging settled metal particles upwardly along the wall. Rake 99 is then lifted away from wall 98, moved downwardly along wall 98 while spaced above the wall, then lowered against wall 98. The rake is then again moved upwardly along the wall to repeat the cycle.

The metal particles are progressively moved upwardly by rake 99 along bottom wall 98, out of liquid body 66 and onto an exposed portion of wall 98 which forms a drainage deck 106. The particles are dewatered on deck 106, the water flowing down the deck and back into liquid body 66. A water spray header 108 directs a small spray of clean water onto drainage deck 106 to wash slimes back into liquid body 66. Rake 99 discharges metal particles as underflow over the upper end of the deck, as shown by arrow 1 10.

The overflow from liquid body 66 passes over weir 64 into liquid body 68 (FIG. 4), which has a lower surface level than liquid body 66. The overflow from classifier 40 is combined in liquid body 68 with the overflow from the turbulators, which passes from header 96 into a distributing trough 112 (FIG. 3) located above classifier 48. Material in trough 112 drains through orifices 114 in the trough bottom wall into the liquid body 68 in classifier 48. Further desliming is efiected in classifier 48, with relatively heavy particles being raked upwardly and out of liquid body 68 and over a drainage deck 115 by a rake 116 in the fashion discussed in connection with rake 99. Overflow from liquid body 68 passes over end wall 118 (FIG. 4), which forms a weir. The overflow is rich in nickel which can, if desired, be recovered eg by dewatering and magnetic separation to produce a nickel-rich concentrate. The underflow raked from the bottom of classifier 48 contains the bulk of the abrasive particles, and some lighter metal particles carried out with the turbulator overflow. The underflow from classifier 48 can, if desired, be treated for recovery of valuables. For example, the underflow can be dried and screened. The oversize from the screen contains an appreciable amount of metal particles, and in effect forms a secondary concentrate. The undersize contains the bulk of the abrasive grits and also contains some metal particles, and can be treated for recovery of abrasive materials and metal particles.

Dewatered underflow from classifier 40 can, if desired, be further dewatered in a conventional dewater densifier. In any event, the dewatered metal particles are passed to rotary dryer 56 (FIGS. 5,6), being received in a hopper 120. Dryer 56 includes a rotary cylindrical member or kiln 122 which is tilted slightly downwardly from a feed end portion 124 to discharge end portion 126. At feed end portion 124 is located a burner 128, which is surrounded by a cylindrical combustion chamber 130. Combustion chamber includes

openings

131, 132 respectively formed on its opposite ends. Burner 128 is directed into the feed end portion of kiln 122 through opening 132, and through an opening 133 formed in the kiln. Feed bin 120 discharges into kiln 122 through opening 133.

At discharge end portion 126 of kiln 122 is a collecting bin 134 having a bottom closure 136. The closure can be selectively opened for removal of dry metal particles. A gas exhaust conduit 138 communicates with the interior of discharge bin 134 through the bin top wall. Conduit 138 communicates with a blower 140, which is located in a vent conduit 146 emerging from a cyclone separator 144. Blower 140 induces ambient air to flow into opening 131 in the combustion chamber at the feed end portion of kiln 122. The incoming air is heated by burner 128 and combined with combustion gases to form a hot gas blast which passes axially through the kiln and dries the metal particles and piggyback slimes with which the particles are coated.

A plurality of axially elongated, radially inwardly extending and radially spaced-apart vanes 142 are mounted on the inside walls of the kiln. The vanes thoroughly sift and agitate the metal particles as the kiln rotates, for complete exposure of the particles to the hot gas blast. The agitation and hot gas blast break the dried slimes from the metal particles, and break up the dried slimes so that the gas blast entrains them as dust and carries them away from the particles and out through vent conduit 138. Entrained dust is separated from the gas in cyclone separator 144. The gas is vented to atmosphere through conduit 146, and the dust is collected in the bottom of cyclone 144 for removal at 148 and discard.

Dry, clean metal particles discharged into collecting bin 134 are removed by opening closure 136, and transferred to a briquetting press (not shown), which can be of any suitable type of conventional design.

EXAMPLE 100,000 pounds of residues produced by grinding slabs and like objects of 18-8 stainless steel (containing 17% Cr, 7% Ni) are passed through a 2 inch vibrating screen for removal of lumps. The residues contain about 70 percent metallics and about 30 percent nonmetallics. The nonmetallics include about 8 percent (by weight of the residues) of hydrochloric acid-insolubles, which consist essentially of grinding wheel abrasives. The remainder of the nonmetallics are essentially sulfur-containing grinding wheel binder and/or decomposition products thereof, and oxides of iron and chromium. The residues contain about 0.25% S.

The screened residues are fed at a rate of 10,000 pounds per hour with 24 gallons per minute of water to a rod mill. The rod mill is 6.5 feet in diameter and 12 feet long, and is charged to 40 percent of its volume with 55,000 pounds of type 1090 carbon steel grinding rods. There are about 25,800 pounds of 4 inch rods and about 14,600 pounds each of 3.5 and 3 inch rods. The mill has a 300 horsepower motor, and rotates at a constant speed of about 21 revolutions per minute.

The residue and water feed rates are controlled to produce a pulp having a density of 50 percent solids by weight. Power input to the rod mill is established at 30 kilowatt hours per ton of residues ground, with continuous feed of water and residues to the mill and continuous discharge of pulp.

The mill discharge is alternately passed to each of two parallel-flow turbulators. Rising current velocity in each turbulator averages 17 to 20 feet per minute. Water is supplied through the water input conduit to each turbulator at a rate of 48 gallons per minute.

Metal particles separated from contaminants in the turbulators are dumped into a rake classifier, and are raked out and dewatered until they contain 20 percent moisture. The dewatered metal particles are passed through a rotary dryer 7 feet in diameter and 44 feet long with a 40 horsepower fan located at the discharge bin and having blades 6 feet in diameter. The dryer is operated at a stack temperature of 350 F with temperature in the combustion chamber within a range of 400 to 800 F., preferably 500 F.

The particles are passed through the kiln, dried, and recovered as a concentrate which is formed into briquettes in a 300,000 pound briquetting press. The briquettes are pillowshaped, each weighting about one-fourth pound.

The concentrate contains 98% metallics, contrasted with the 70 percent metallics in the feed material. Sulfur is reduced to 0.04 percent, and hydrochloric acid-insolubles to 2 percent, so the briquettes are satisfactory for use in electric-arc and other steelmaking processes. For example, the briquettes can be used as high-purity scrap in furnace charges, or as coolant for superheated melts. The chromium content is 17 percent, and the nickel concentration is 9 percent.

Grinding residues of alloy steels other than stainless steels can be treated for reclamation of metal particles in accordance with the invention. The term alloy steels as used herein includes stainless steels (which contain at least 4 percent chromium) and also includes those steels defined as alloy steels by the American Iron and Steel Institute. Such steels have at least 1.65% Mn, 0.6% Si, 0.6% Cu, or a definite minimum of any other alloying element added to produce desired properties. Grinding residues of metals can be processed for reclamation of metal particles whenever the worth of the base metal and/or alloying constituents makes reclamation desirable. The inventive system is applicable to grinding residues of nonferrous as well as ferrous metals. While being particularly advantageous in application to grinding residues, principles of the invention can also be advantageously employed with other mixtures of elemental metallics and contaminants, and to still other feed materials containing metal values (elemental or nonelemental) and contaminants where selective grinding, continuous grinding mill operation, and/or hydroclassification as described herein are desirable. Thus, although the invention has been described in connection with a preferred embodiment, modifications of the preferred embodiment can be made without departing from principles of the invention. Such modifications are within the scope of the appended claims.

I claim:

1. Process for recovering metal particles, comprising providing material containing metal particles and nonmetallic contaminants mixed with the metal particles, subjecting the material to a grinding operation, maintaining power input to the grinding operation at a magnitude to pulverize the nonmetallic contaminants while minimizing work hardening of the metal particles,

separating metal particles from pulverized contaminants,

and

recovering separated metal particles.

2. The process of claim 1, including briquetting recovered metal particles,

the metal particles being cohered in the briquetting by flow of metal of the particles.

3. Process for recovering metal values, comprising providing material containing metal values and contaminants,

forming a pulp of the material and subjecting the material to a grinding operation in the pulp by contact with grinding rods in a rod mill,

continuously feeding material to the grinding operation,

continuously discharging ground material from the grinding operation, and

maintaining pulp density within a range of about 45 to 55 percent solids by weight.

4. The process of claim 3,

the pulp density being maintained within a range of about 45 to 55 percent solids by weight.

5. The process of claim 1, including forming a pulp of the material,

the material being subjected to the grinding operation in the pulp by contact with grinding rods in a rod mill,

continuously feeding material to the grinding operation,

continuously discharging ground material from the grinding operation, and

maintaining pulp density at a magnitude not greater than about 60 percent solids by weight.

6. The process of claim 1,

the metal particles being steel particles,

the power input to the grinding operation being maintained within a range of about 20 to 40 kilowatt hours per ton of material ground.

7. Process for recovering metal values, comprising providing material containing metal values and contaminants,

subjecting the material to a grinding operation,

maintaining power input to the grinding operation at a magnitude to pulverize the contaminants while minimizing grinding action on the metal values,

separating metal values from pulverized contaminants, and

recovering separated metal values,

the metal values being separated from the pulverized contaminants by passing ground material from the grinding operation into an upwardly flowing liquid stream to separate light particles from heavy particles.

8. The process of claim 5, including continuously feeding material to the grinding operation,

continuously discharging ground material from the grinding operation, and

alternately terminating passage of ground material into the upwardly flowing liquid stream and initiating passage of ground material into a second upwardly flowing liquid stream.

9. Process for recovering metal particles from grinding residues, comprising providing grinding residues containing metal particles and nonmetallic contaminants mixed with the metal particles,

subjecting the residues to a grinding operation,

controlling the grinding operation to pulverize the nonmetallic contaminants while minimizing work hardening of the metal particles,

separating metal particles from pulverized contaminants,

and

recovering separated metal particles.

10. The process of claim 8, including forming a pulp of the grinding residues,

the grinding residues being subjected to the grinding operation in the pulp by contact with grinding rods in a rod mill,

continuously feeding material to the grinding operation,

continuously discharging ground material from the grinding operation, and

11. The process of claim 10,

12. The process of claim 1 l,

the pulp density being maintained at about 50 percent solids by weight.

13. The process of claim 8,

the metal particles being steel particles, and

the grinding operation being controlled by maintaining power input within a range of about 20 to 40 kilowatt hours per ton of material ground.

14. The process of claim 13,

the power input being maintained at about 30 kilowatt hours per ton of material ground.

15. The process of claim 8,

the metal particles being separated from the pulverized contaminants by passing ground grinding residues into an upwardly flowing liquid stream to separate light particulate material from heavy particulate material.

16. The process of claim 15,

the metal particles being steel particles, and

the upwardly flowing liquid stream having a rising current velocity within a range of about to 35 feet per minute.

17. The process of claim 15, including passing the heavy particles downwardly in the upwardly flowing liquid stream, and

discharging heavy particles into a liquid body for settling to the bottom portion of the liquid body,

removing settled heavy particles from the bottom portion of the liquid body, and

overflowing slime-containing liquid from the top portion of the liquid body.

18. The process of claim 15, including continuously feeding material to the grinding operation,

continuously discharging ground material from the grinding operation,

passing the heavy particles downwardly in the upwardly flowing liquid stream into a storage area,

holding the downwardly passed heavy particles in the storage area, and

terminating passage of ground material into the upwardly flowing liquid stream, initiating passage of ground material into a second upwardly flowing liquid stream, and initiating discharge of stored heavy particles from the storage area.

19. The process of claim 8,

the nonmetallic contaminants including grinding whee] abrasive and binder components.

20. The process of claim 19,

a portion of the grinding wheel components being adhered to the metal particles.

21. The process of claim 19,

the grinding wheel binder containing sulfur.

22. The process of claim 19,

the grinding wheel abrasive including a material selected from the group consisting of alumina and silicon carbide.

23. The process of claim 8,

the metal particles being alloy steel particles.

24. The process of claim 23,

the metal particles being stainless steel particles.

25. The process of claim 8,

the pulverized contaminants being separated from the metal particles by hydraulic classification,

the separated metal particles being covered with slime, and

the separated metal particles being subjected to a hot gas blast to dry the slime and separate dried slime from the metal particles.

26. The process of claim 8, including briquetting recovered metal particles,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Fail; 3 .657,997 Dated April 25 V1972 In az Vincent A. Vellella I: is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

F I l Column 8, line 11, change "3" to 5--.

Column 8, line 41, change "5" to -7. Column 8, line 60, change "8" to 9-. Column 9, line 1, change "8 to -9-.

Column 9, line 9, change "8" to --9-.

Column 10, line 7, change "8"to --9-. Column 10, line 18, change "8" to -9-. Column 10, line 22, change "8" to -9--. Column 10, line 29, change "8" to -9--.

Signed and sealed this 19th dayoi september 1972.

(SEAL) A ttest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents

Claims

2. The process of claim 1, including briquetting recovered metal particles, the metal particles being cohered in the briquetting by flow of metal of the particles.
3. Process for recovering metal values, comprising providing material containing metal values and contaminants, forming a pulp of the material and subjecting the material to a grinding operation in the pulp by contact with grinding rods in a rod mill, continuously feeding material to the grinding operation, continuously discharging ground material from the grinding operation, and maintaining pulp density within a range of about 45 to 55 percent solids by weight.
4. The process of claim 3, the pulp density being maintained within a range of about 45 to 55 percent solids by weight.
5. The process of claim 1, including forming a pulp of the material, the material being subjected to the grinding operation in the pulp by contact with grinding rods in a rod mill, continuously feeding material to the grinding operation, continuously discharging ground material from the grinding operation, and maintaining pulp density at a magnitude not greater than about 60 percent solids by weight.
6. The process of claim 1, the metal particles being steel particles, the power input to the grinding operation being maintained within a range of about 20 to 40 kilowatt hours per ton of material ground.
7. Process for recovering metal values, comprising providing material containing metal values and contaminants, subjecting the material to a grinding operation, maintaining power input to the grinding operation at a magnitude to pulverize the contaminants while minimizing grinding action on the metal values, separating metal values from pulverized contaminants, and recovering separated metal values, the metal values being separated from the pulverized contaminants by passing ground material from the grinding operation into an upwardly flowing liquid stream to separate light particles from heavy particles.
8. The process of claim 5, including continuously feeding material to the grinding operation, continuously discharging ground material from the grinding operation, and alternately terminating passage of ground material into the upwardly flowing liquid stream and initiating passage of ground material into a second upwardly flowing liquid stream.
9. Process for recovering metal particles from grinding residues, comprising providing grinding residues containing metal particles and nonmetallic contaminants mixed with the metal particles, subjecting the residues to a grinding operation, controlling the grinding operation to pulverize the nonmetallic contaminants while minimizing work hardening of the metal particles, separating metal particles from pulverized contaminants, and recovering separated metal particles.
10. The process of claim 8, including forming a pulp of the grinding residues, the grinding residues being subjected to the grinding operation in the pulp by contact with grinding rods in a rod mill, continuously feeding material to the grinding operation, continuously discharging ground material from the grinding operation, and maintaining pulp density at a magnitude not greater than about 60 percent solids by weight.
11. The process of claim 10, the pulp density being maintained within a range of about 45 to 55 percent solids by weight.
12. The process of claim 11, the pulp density being maintained at about 50 percent solids by weight.
13. The process of claim 8, the metal particles being steel particles, and the grinding operation being controlled by maintaining power input within a range of about 20 to 40 kilowatt hours per ton of material ground.
14. The process of claim 13, the power input being maintained at about 30 kilowatt hours per ton of material ground.
15. The process of claim 8, the metal particles being separated from the pulverized contaminants by passing ground grinding residues into an upwardly flowing liquid stream to separate light particulate material from heavy particulate material.
16. The process of claim 15, the metal particles being steel particles, and the upwardly flowing liquid stream having a rising current velocity within a range of about 15 to 35 feet per minute.
17. The Process of claim 15, including passing the heavy particles downwardly in the upwardly flowing liquid stream, and discharging heavy particles into a liquid body for settling to the bottom portion of the liquid body, removing settled heavy particles from the bottom portion of the liquid body, and overflowing slime-containing liquid from the top portion of the liquid body.
18. The process of claim 15, including continuously feeding material to the grinding operation, continuously discharging ground material from the grinding operation, passing the heavy particles downwardly in the upwardly flowing liquid stream into a storage area, holding the downwardly passed heavy particles in the storage area, and terminating passage of ground material into the upwardly flowing liquid stream, initiating passage of ground material into a second upwardly flowing liquid stream, and initiating discharge of stored heavy particles from the storage area.
19. The process of claim 8, the nonmetallic contaminants including grinding wheel abrasive and binder components.
20. The process of claim 19, a portion of the grinding wheel components being adhered to the metal particles.
21. The process of claim 19, the grinding wheel binder containing sulfur.
22. The process of claim 19, the grinding wheel abrasive including a material selected from the group consisting of alumina and silicon carbide.
23. The process of claim 8, the metal particles being alloy steel particles.
24. The process of claim 23, the metal particles being stainless steel particles.
25. The process of claim 8, the pulverized contaminants being separated from the metal particles by hydraulic classification, the separated metal particles being covered with slime, and the separated metal particles being subjected to a hot gas blast to dry the slime and separate dried slime from the metal particles.
26. The process of claim 8, including briquetting recovered metal particles, the metal particles being cohered in the briquetting by flow of metal of the particles.