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ABSTRACT

A concentration process of zinc silicated minerals, particularly willemite and calamine concentration, by single operations, or conventional steps of ore treatment, some of which include the following: Preparation of stockpiles of different mineralogical and contents compositions, crushing, screening, storage, dense separation, washing, homogenization, magnetic separation, grinding, classification, rubbing, conditioning, flotation, thickening, filtering, calcination, storage and waste deposition.

Inventor: Julio Cesar Bittencourt
Original Assignee: Compamhia Mineira de Metais
Section: Performing Operations; Transporting
Classification: Separation Of Solid Materials Using Liquids Or Using Pneumatic Tables Or Jigs; Magnetic Or Electrostatic Separation Of Solid Materials From Solid Materials Or Fluids; Separation By High-voltage Electric Fields

This invention deals with the concentration process of zinc silicated minerals, particularly the willemite and calamine concentration conducted by single operations or conventional steps of ore treatment, some of which include the following: The preparation of stockpiles with different mineralogical and contents compositions, crushing, screening, storage, dense separation, washing, homogenization, magnetic separation, grinding, classification, rubbing, conditioning, flotation, thickening, filtering, calcination, storage and waste deposition.

This invention deals with product and concentration/calcination process of zinc silicated minerals, particularly willemite and/or calamine, prior to hydrometallurgical processing, i.e., beneficiation of the ore to treat using hydrometallurgical processes.

Willemite is a zinc silicate, Zn2SiO4, that sometimes contains manganese and is found in the form of prismatic crystals or grained masses, often yellowish green, sometimes white, brown, or red. Investigation has found that willemite is an ore formed from the metamorphism of other secondary ores: Smithsonite and hemimorphite. The latter is also known as calamine. Calamine or hemimorphite—a hydrated zinc basic silicate, Zn4Si2O7(OH)2H2O—is found in the form of white silicate, which is one of the most important zinc ores. Smithsonite, on the other hand, is a mineral that is formed from modified sphalerite, Zn S, known in nature in the form of zinc carbonate (ZnCO3).

The concentration processes of zinc ores are well known. One of such processes, referred to as the “dense process,” will benefit willemite with 20 percent of zinc, and the other, the “volatilization process,” will convert calamine into oxide starting from 12 percent of zinc to nearly 50 percent of zinc in Waelz oxide (known because of the process using a Waelz kiln). The dense process is limited in terms of production, granulometry and recovery, and it will only treat high content willemite. In connection with Waelz kilns, in addition to production limits and because it will only treat calamine, it is highly costly, notwithstanding its increased output.

The Petitioner has developed a concentration/calcination process of zinc silicated minerals with single, unique, new characteristics in that it will make beneficiation uniform regardless of the ores to be treated and under which both ores may be treated either individually or mixed and higher output and efficiency may be achieved—over 85 percent with flotation—at lower final beneficiation costs. Depending on the willemite content to be treated, over 20 percent of zinc, the dense process may be used as a supplement of the flotation process. In addition to joint flotation, the process will require calcination for removal of flotation reagents and organic materials that form frothing in hydrometallurgy, resulting in production and efficiency losses of the cathode.

The Petitioner has developed a concentration/calcination process of zinc silicated minerals that is characterized by the following stages, as shown in the block diagrams attached herewith (FIGS. 1, 2, 3 and 4):

(a) crushing (1) (2): Crushing to diminish ore block diameters from nearly 560 to 38 mm for calamine and nearly 560 to 15 mm for willemite; alternately, the ore may pass through scalp previously.

(b) screening (3) (7) (9): In open and closed circuit with crushing, to preferentially feed grinding 100 percent shorter than nearly 60 mm to nearly 15 mm in diameter of the ore to be treated.

(c) storage (4) (5) and dense separation, optional: Using revolving drum and sieve.

(d) washing (6): Conventional, under which unders from the trommel are directed to spiral classifiers (10) and from here lump, along with materials caught by the screen (3) (7) (9), are directed to grinding (13) and classification (14) and fines to deslurrying (15), and, alternately, to homogenization and magnetic separation.

(e) grinding (13): Granulometry material is obtained at nearly 80 to 100 percent under 210 microns, that may be directed to rubbing or flotation, or may be deslurried, lump from hydroclone is fed into flotation, and fines are directed to a sump; alternately, sieve lump (7) may be directed to the sieve (9) for further crushing (8) and a new classification.

(f) deslurrying: Primary (15), secondary (16), tertiary (17), quaternary (18).

(g) rubbing (as appropriate): Of pulp, using equipment operating at around 1500 rpm with 50 to 75 percent pulp weight solids for 30 to nearly 60 minutes.

(h) conditioning and additive addition (19) (20): Ore pulps receive additives prior to flotation, firstly pH modifiers, activators, then collectors, frothers, and alternately, dispersants and others.

(i) flotation (21) (22) (23) (24) (25): The pulp may undergo, alternately, one or more magnetic separation stages, before, during or after flotation, which may be conducted on conventional or column cells, consisting of one or more rougher stages (21), two or more scavengers stages (22) (23), and one or more cleaner stages (24), and cleaner scavengers (25).

(j) thickening (27): Concentrates from the different ores were joined to form the final concentrate, which is pumped into one or more thickeners (27), where it receives one or more flocculants at an amount that may range from around 15 to 50 g/t of dry concentrate.

(k) filtering (28): Thickener underflow (27) is filtered and the overflow, after thickening (29), forms an underflow, filtering, and an overflow that is settled on the fine concentrate sump. The cake is directed to calcination (31).

(l) calcination (31): The wet cake is fed at a rate that may range from around 500 to 750 t/day wet on the furnace, inner temperature ranging from around 500 to 1000° C. at the hot zone.

(m) storage.

1. As shown in FIG. 1 and FIG. 2 attached herewith, crushing (1) (2) (8) is conducted using crushers of the jaw, revolving, roller, hammer, or other type, capable of reducing the 1 m ore blocks to nearly 6.5 mm. Crushers of the jaw, revolving, roller, hammer or other type are preferentially used to reduce blocks to the desired diameters, for instance, to reduce approximately 560 mm to 38 mm for calamine and approximately 560 mm to 15 mm for willemite. In order to minimize crusher operation, a vibrating or fixed grid may be mounted before the crusher as a scalp for the material lower than the desired size. Screenings (3) (7) (9) are conducted using vibrating or bend horizontal screens with square, circular, rectangular, or oblong openings; square screens are preferred for approximately 3 to 0.25 inch openings. The material is crushed (1) (2) (8), screened (3) (3) (7) in open and closed circuit to feed grinding (13) 100 percent shorter than nearly 38 mm for calamine and nearly 18 mm for willemite. Next, the crushed calamine ore (FIG. 1) is washed in a revolving drum (6) and conventional sieve (7) with 2 mm screen, the unders from washer trommel are gravity discharged into the spiral classifier (10), from which overs, along with materials caught by the screen (7), are directed to the grinding bin (12) and grinding (13); unders from 2 mm screen are pumped into washer feed. Fines from spiral classifier are directed to secondary deslurrying (16), from which lump is directed to tertiary deslurrying (17), from which lump travels to the quaternary one (18). Fines from tertiary deslurrying may be recycled or dumped into mud sumps, along with fines from quaternary deslurrying (18), for reuse later. Calamine ore deslurrying may be conducted in two or more stages for fines harmful to flotation to be discarded; this is made using 6″ to 1″ hydroclones, with d50 ranging from 5 microns to nearly 0.5 microns, depending on the ore, or even using microscreens.

Likewise, willemite, depending on the ore, will pass through this same washing process (6) and deslurrying for removal of fines harmful to flotation. Willemite ore (FIG. 2) is wet classified on the two-deck 18 mm and 2 mm sieve, and lump larger than 18 mm is re-crushed by the tertiary crusher (8), dry closed with a 18 mm sieve (9); fines, 2 mm unders, are gravity discharged into the spiral classifier (10), which underflow is directed by a belt conveyor to the pile along with those shorter than 18 mm from the sieve (9); the overflow is pumped into the secondary calamine deslurrying (16). Only washing is usually performed, which fines are joined with those of calamine at the secondary deslurrying (16). These fines go through grinding (13) and/or rubbing (optional), as needed, depending on the appearance of the ore mineral surface. It is worth noting that, if fines are not present, the washing line part will not be used, and the ore will be directly conveyed to the dry sieve (7), using the same recrusher (8) screen deck (9). Additionally, depending on the ore, wire or plastic screen may be used with 12 to 25 mm mesh.

For grinding (13) ore, dry or wet autogenous, half-autogenous, or revolving, bar and/or ball, roller, vibrating, tower or vertical, or pendulum mills may be used in closed or open circuits, with spiral classifiers or hydroclones (14), or vibrating screens, the use of revolving ball mill (13) in closed circuit with hydroclones is preferred. The granulometry of the material produced by grinding is nearly 90 percent under 210 microns for both willemite and calamine. For willemite (FIG. 2), grinding output will often directly feed rubbing (optional) or flotation (21); for calamine (FIG. 1), this product is deslurried with lump from hydroclone (14), and feeds flotation (21); fines are directed to sump. Next, depending on the presence of clay film and/or iron oxide and/or other materials on willemite or calamine mineral surfaces, the pulp is rubbed using an attrition equipment operating at around 1500 rpm, with nearly 50 to 75 percent pulp weight solids, for 30 min to nearly 60 min. Depending on the ore, a flotation operation may be conducted, as appropriate, using a unit cell that is stirred by compressed air or an stirring mechanism on the grinding hydroclone underflow (14), for both calamine and willemite; in this case the reagents are the same, the concentrate from this flotation will be pumped into the flotation circuit and the waste will be recycled to the mill (13) to form its circulating load.

Calamine ore deslurrying is conducted in two to four stages for fines harmful to flotation to be discarded; this is made using 12″ to 1″ hydroclones, with d50 ranging from 5 microns to nearly 0.5 microns, depending on ore, or even using microscreens; use of four deslurrying operations is preferred, with hydroclones in 5″ or 6″, 4″ or 5″, 1″ or 2″ and 1″ or 2″ diameters for primary (15), secondary (16), tertiary (17) and quaternary (18) deslurrying respectively.

Likewise, willemite ore, depending on its origin, is previously deslurried or washed (6), as described earlier, at the tertiary crushing for fines to be discarded, 100 percent under nearly 0.5 microns using equipment similar to that of calamine. Dense concentration is conducted as needed, with an intermediate medium consisting of ferrosilicon or magnetite pulp, or mixes of dense liquids to form the intermediate density between the density of willemite or calamine particles and the gangue ones; use of ferrosilicon pulp is preferred

Likewise, the pulp is subjected, as needed, to one or more magnetic separation stages, before, during or after flotation, by using wet or dry low, mid, or high intensity magnetic field separators and variable gradients with the quantity of diamagnetic ores; use of wet low intensity separators is preferred.

Prior to flotation, willemite and calamine ore pulps receive reagents and are contained in conventional stirring tanks (19) (20) for 1 min to 60 min, depending on the ore. Such pH modifiers and activators are used as sodium, potassium, barium, or ammonia sulfides purely or mixed, with or without caustic soda and/or sodium carbonate; the consumption of sulfide ranges from nearly 1500 to nearly 4000 g/t of dry ore for willemite and nearly 2500 to nearly 5000 g/t of dry ore for calamine, where 2000 to 3000 g/t for willemite and 3000 to 4500 g/t of calamine is consumed preferentially; more preferentially, 2200 to 2700 g/t for willemite and 3400 a 4100 g/t for calamine is consumed.

Preferentially, sodium carbonate is used for consumption of nearly 800 g/t of dry ore to nearly 1500 g/t of willemite dry ore and nearly 1200 g/t of dry ore to nearly 2000 g/t of calamine ore. Pulp pH will change based on the ore, and may range from nearly 10 and 12.5 for willemite and calamine.

Next, the pulp is contained again and receives one or more collectors that may be primary, or secondary amines, or mixes thereof, in varying proportions and depending on the ore, and may range from 180 to 350 g/t of dry ore for willemite and of 300 a 500 g/t of dry ore for calamine. Next, the pulp receives one or more frothers that may be aliphatic alcohols, preferentially methyl isobutyl carbinol or similar, which consumption ranges from 20 to 60 g/t of willemite or calamine dry ore, 30 to 50 g/t of willemite or calamine dry ore being preferred.

Because it consists of finer grains, the calamine pulp receives one or more dispersants such as sodium hexametaphosphate or similar in varying proportions from nearly 150 to nearly 400 g/t of dry ore; 200 to 350 g/t of dry ore is preferred.

Calamine flotation is conducted on conventional or column cells consisting of one rougher (21), two scavengers (22) (23) and one cleaner (24) stage. Scavengers concentrates are recirculated, from the second to the first one and then to the rougher cells. Waste from the last scavenger will form calamine waste, that is directed to the sump. The rougher concentrate is fed into the cleaner cell, which waste is recirculated into the rougher feed. The cleaner concentrate will form calamine concentrate. Willemite flotation consists of two circuits, one for breakdown, rougher (21) and scavenger (22), the other for cleaning, cleaner (24) and cleaner scavenger (25). The cleaner waste is recirculated into the rougher feed. The concentrate scavenger recirculates into the rougher feed. The cleaner concentrate will form willemite concentrate. The willemite flotation control panel is provided with a PLC electronic system to monitor the operation of the cells of both willemite lines.

Willemite and calamine concentrates are joined in a tank (26) to form the final concentrate that is pumped into one or more thickeners (27), where one or more flocculants are added that may be, for instance, polyacrylamide or similar, in proportions of about 15 to 50 g/t of dry concentrate; thickener underflow (27) is filtered (28) by press type rotary vacuum drum, disc, table filters, the revolving drum being preferred. Overflow is gravity discharged to the thicker (29), that may receive filter medium wash water and powder depletion pulp from the calcining furnace pile (refer to FIG. 3 attached herewith); thickener underflow (29) is pumped into the concentrate mix tank (26), and the overflow is recycled at the willemite conditioner (20) outlet and/or settled on the sump (basin) of fines for future reuse. The filter (28) forms two products: The filtered material that is sent back to thickening (29) and the cake that is directed to calcination (31). The calcining process (31), as shown in FIG. 3 attached herewith, consists of a revolving furnace (31), fan (35) and electrostatic filter (32) for recovery of exhaust gas fines, stack (33), cyclones (35), sleeve filters (36), cooler (37), crusher (38), BPF oil heater assembly (34), BPF oil storage/supply system, burning torch system, vapor generation system. The wet cake (with 12 to 16 percent of water) is fed at a rate that ranges from 500 to 850 t/day wet, on the revolving furnace (31), inner temperature ranging from 500 to 1200° C. at the hot zone. Organic materials and water after burned are sucked at the other end of the furnace to the stack through the electrostatic filter for recovery of fines. The calcine concentrate produced at the other end of the furnace (31), where the torch is placed, is gravity discharged into the cooler (37), and receives water to decrease temperature from nearly 600° C. to nearly 80° C., then alternately to a crusher. To improve calcined quality the furnace discharge zone is sucked by blowing air and then cycloning (35), where two products are generated: Lump that is settled as final product and fines that are directed to the sleeve filter (36) along with air. The sleeve filter product joins the lump from the cyclone by way of a rotary valve; clean air is ousted by the filter stack. Most of the produced concentrate is discharged through the cooler into the crusher, that may be of the roller, jaw, or hammer type; the latter is preferred in order to reduce any sticks in the calcined material. From the crusher discharge the calcined material is carried by a bucket hoist to a storage shed where a lower discharge reset and belt conveyor system loading into trucks is conducted. Calcine concentrate humidity ranges from nearly 3 to 7 percent and is formed at the final product of the whole process. BPF type 2A oil is used for the furnace—type up to 7A may also be used. Depending on local conditions other fuels may be used, where available: charcoal or coal, hard coke and others. For both storage and use of oil 2A, a vapor generation system is provided, BPF oil boilers as well, for control of viscosity and temperature around 65° C., and maintenance of storage and pumping into the daily tank. Next, the oil is heated by electric resistances to 150° C. and is pumped 18 kgf/cm2 pressure. This temperature and pressure are kept automatically for setting the torch. The heated pressurized oil is mixed on the torch with vapor at 9 to 11 kgf/cm2 pressure for atomization and composition of the flame that is adjusted by primary air that is subdivided into two inlets, radial and axial air. An automatic control is provided for depression of furnace hot and cool interdependent zones that are linked to the temperatures in the smoke chamber and electrofilter outlet so as to keep the temperature at the electrofilter inlet as high as possible. To increase or diminish depressions at the fan inlet a wide range lattice valve is mounted before the fan. Operating peripherals such as automatic uncloggers, temperature, pressure and other controls are provided all along the furnace circuit. The main CO and O2 is monitored by an automatic control at the electrofilter inlet, that is provided with relief doors to check for CO buildup at safety levels. Before the electrofilter a combustion gas cooling tower is provided that may be bypassed where increased temperature is desired. The furnace control panel is provided with a PLC to automatically control each operation. Furnace revolution may range from 0 to 5.0 rpm, 1.0 rpm being the most usual. In addition to the main motor and auxiliary diesel motor is provided to guarantee power supply.

The final moisture content of the final product based on concentrate zinc silicates ranges from nearly 3 to 7 percent and zinc contents from nearly 42 to 47 percent in mass.

The following are examples illustrating the invention that should not be taken as a reference for purposes of restricting the patent.

EXAMPLE 1


Willemite ore was fed at a rate of 120 t/h on the primary crusher, then on the secondary crusher, closed with 2½″ vibrating screen with, piled 100 percent under this size, then reloaded to feed the washer, and received water, then screened at washer outlet for removal of the fines that have been pumped into the 2nd calamine deslurrying. Lump from the washer was dry re-crushed in closed circuit with the 15 mm vibrating screen and tripper homogenized on the homogenization pile. Next, it was reloaded at a rate of 80 t/h, equally divided into two grinding circuits operating with hydroclones to produce pulp with 95 percent under 65 mesh Tyler. Solids were set to 32 weight percent in the product. Next, pulp was conditioned and pH activator and regulator was added in proportions of 1520 g/t and 196 g/t of collector, to feed two identical flotation lines, which circuit was described earlier, where further reagents, 940 g/t of sulfide, 40 g/t of frother and 90 g/t of collector were added. The final concentrate with 43.5 percent of zinc contents was directed to filtration along with the calamine one.

Calamine ore was fed at a rate of 120 t/h on the primary crusher, then on the secondary crusher, closed with a 1½″ vibrating screen, piled 100 percent under this size, then reloaded to feed the washer at a rate of 37.4 t/h, received water, was screened at the washer outlet to feed the spiral classifier and deslurrying operations as described earlier. Slump from the washer (13.8 t/h) and spiral classifier (11.3 t/h) were directed to the grinding circuit, closed with hydroclone to be cut down 100 percent shorter than 65 mesh Tyler. The fines from the spiral classifier (12.3 t/h) and willemite slurry mud (3 t/h) were directed to 5″ hydroclones of the secondary deslurrying at 2 to 2.5 kgf/cm2 pressure, the underflow of which (11.4 t/h) being directed to the conditioning tank and the overflow gravity directed to the recovery sump for future processing in tertiary and quaternary deslurrying operations. The grinding hydroclone overflow (12.6 t/h) was pumped at 2 to 2,5 kgf/cm2 pressure to the primary deslurrying hydroclones, which overflow was directed the secondary deslurrying (25.1 t/h) and its underflow(18.3 t/h) was joined with the product from the secondary deslurrying, then both were finally conditioned and received reagents, dispersant at 277 g/t, activator at 2000 g/t, collector at 150 g/t and frother at 40 g/t. The flotation circuit is as described earlier, except that in this example no rougher concentrate cleaning was used, which, alone, had 38 percent of zinc. Zinc recovery up to flotation for willemite was 81 percent and 72 percent for calamine in connection with the fed zinc. Next, both concentrates were mixed and filtered, resulting in contents of 42 percent of zinc and production of 22.8 t/h and 15 percent of cake moisture. Next, this concentrate was calcined along with the concentrate stored at the filtering house, resulting in calcine concentrate with 44.5 percent of zinc, final recovery of 78 percent, 5 percent moisture. This concentrate was directed to metallurgy for production of metallic zinc.

EXAMPLE 2


FIG. 4 attached herewith illustrates the operation of a simplified calamine and/or willemite beneficiation plant.

At first, both calamine and willemite beneficiation plants are separated. The single operations in the stages of crushing, washing, grinding and flotation are shown for both calamine and willemite. Flotation wastes from both calamine and willemite are collected and directed to the waste sump or settling basins for recycling of mud. Concentrates from the flotation step for both calamine and willemite are joined in the final homogenization tank of willemite from the flotation step, then the resulting mix is directed to common stages of filtration and calcination.