CA1143166A - Recovery of nickel and other metallic values from waste - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Nickel and other metal values are recovered from waste materials such as those generated during the production of stainless steels. Various waste forms such as mill scale and flue dusts are blended with a carbonaceous reductant and pelletized. The pellets are subjected to a reduction roast followed by melting to provide the metal values.

Description

FIELD OF THE INVENTION
The present invention relates to the recovery of nickel and other metal values from production waste materials.

BACKGRO~ND OF THE INVENTION
.
Large amounts of waste materials are formed during the production of stainless steel and other alloyed metals.
Waste materials such as mill scale, pickling liquor, dust, oily grindings and swarf are generally considered to have relatively little value and consequently are assigned to use as land fill or are disposed of by other means. This is economically unrewarding and, equally important, does not conserve valuable metals such as nickel, molybdenum and chromium.
There are a number of methods presently known for recovering metal values from wastes as well as several pro-cesses dealing with the production of metallic elements rom ores. However, such processes differ considerably from the present invention.
For example, in one of the most recent proposals regarding the treatment of stainless steel making waste in which a carbonaceous reductant is employed, it is deemed necessary that the feedstock contain appreciable amounts of cement to provide sufficient pellet strength following pelletization.
Until the developemnt of the present invention a number of processes fortherecovery of metal values from wastemateri-al have been disclosed. Among these disclosures are the fol-lowing, all of which fail to perceive the essential steps o~
the present invention, proper blending of ingredients and 3D elimination of the need for a binding or cementing agent.
U.S. Patent 3,264,091, which deals with the pro-cessing of ironore discloses that it is necessary to use "_.. ~.

3:~6~
a flu~ and a hi~h -temperature bonding in order to provi.de strong pelle-ts. In such a process s-trong pellets could not be formed unless the speciEic bo.nding step is carried out.
U S. patent 3,870,507 discloses a process for treat-ing steel making waste in which tarwas used as a binder and a heat treating operation in an oxidizing atmosphere employed in order to provide pellets hav.ing the desired strenyth.
In U.S. Patent 4, 004, 918 the process disc:losed is concerned with the treatment of stainless waste as is the .
process of the presen-t inventlon. ~n this process, organic and inorganic binders are required to form briquettes, car-bonaceous materials are lacking for supplying a reducing atmosphere. Reduction in this process of this patent is : accomplished by heating the briquettes in an electric-arc melting furnace.. Again the present invention process is an importan~ improvement over the disclosure in this patent.
German Auslegeschrift 1,039,546 teaches the use of ferrous hydroxides sludges from spent pickle liquors for briquetting of flue dust and fines from ores. Briquettes are formed and require a binder of fine tar and napthalene adsorbed on the:ferrous hydroxides precipitates present.
U. K. Patent 853, 532 deais with extracting metal values from ores and also discusses the treatment of steel making waste. The process relies on the use of~hydrocarbon oil emulsion and a hydraulic binding agent (e~./ Portland cement) to form pellets.
Until the development of the process of the present invention no one envisioned being able to recover nlckel and other metal values Erom most of the undesirable wastes produced in various metal facilities. Furthermore, until the development of the process of the present invention, it 3~66 was never envisioned that pelletized or briquetted metal wastes could be formed without the use of blinding agents and their ensuing undesirable side effects in further processing.

OBJECT OF T~IE INVENTION
. . .
The present invention aims at providing a process which converts waste from specialty steel mills, such as flue dust, mill scale and swarf, into a useful remelt alloy for the stainless, alloy and specialty steel industries.
A further object of the present invention is to provide a method of pelletizing for the recovery o metal values from waste without the necessity of using bonding agents.

SUMMARY OF THE INVENTION
-According to the present invention, the important disadvantages that have stemmed from the process of the prior art are overcome. It has been found in accordance herewith, and, in fact, one of the most important factors in the success of the present invention, that by using a

2~ proper balance of feedstock ingredients, binding or cement additions are ~uite unnecessary. Specifically, it has now been discovered that by proper selection of metallurgical wastes and blending of these wastes with a carbonaceous material supplying a substantially oxygen free reducing at-mosphere, strong pellets can be produced without the use of binding materials, such pellets can be converted to melting stock highly suitable for tlle production of metal alloys by a re~uction roasting and melting operation.

Generally speaking, the present invention contem-plates a process for reclaiming metallic values from wastes and comprises blending a waste material containing one or more of mill scale, furnace scale, swarf and high-grade grit with a carbonaceous reductant, water and, at times when a high amount of CaO is present, pickle liquor or pickle liquor and water and at least one material selected from the group consisting of furnace flue dust, and process sludge to form a blended feed material, pelletizing said blended feed material to form strongly bound pellets,heating said pellets in the- presence of an oxygen free carbonaceous material not capable of reacting with said waste materials for the purpose of binding but capable of providing a re-ducing atmosphere (particularl~ in accordance with the two stage heating-reducing operation described hexein) t reacting the oxidized metal waste materials of said pellets with said formed reducing atmosphere thereby forming a metal-containing pellet, and thereafter melting said metal-containing pellet to separate and recover a metal value.
For the purpose of convenience, the following de-scription is largely directed to recovery of metal values, e.g., nic~el, chromium, iron, molybdenum, etc., from stain~
less steel wastes; however, it is to be understood that the invention is not restricted to such recovery but is appli-cable to the recovery of metals generally fxom other metal containing wastes, e.g., nickel-containing wastes, copper-containing wastes, ferrous and ferrous allo~ wastes, etc.
It is contemplated that metal-containing pellets formed by the reduction-roasting step could also be used as a supplemental addition to a melt of stainless steel, despite the large amount of gangue contained therein.
Within the melting furnace, it has been found advan-tageous to add su~stances such as burnt lime, limestone, mag-nesia, dplomite and crushed steel-making slag to the charge during melt-down to ease tha separation of ~olten metal from gangue. It is preferred ~o maintain a basic slag in which the ratio of basic constituents, e.g., CaO, MgO, etc., to acid constituents, e.g., sio2~ Al203,etc., be ~etween about 0.8 and 1.8 to insure the desired chromium recovery. For example, using a ratio of 0.6, the chromium recovery was 28%, whereas with a ratio of 1.3, the chromium recovery was 96%.
This ratio can be maintained by the addition of burnt lime dolomite or limestone to the charge within the melting furnace, The amount of burnt lime or other basic rock added to the melting furnace is largely influenced by the lD amount of CaO and MgO present within the pellets. By reason of an appropriate selection and propor~ioning of waste materials as discussed below, it is possible in addition to providing strongly bound pellets, to actually minimize the limestone or other basic additions to the melting furnace by utilizing the CaO in the pellet for such purpose, even though CaO and MgO would have been considered a contaminant. Also, chromium-rich substances, e.g., ferrochrome, chromite oret or, for that matter, nickel-rich substances, e.g., niçkel, nickel oxide, nickel alloys, etc. can be added to the molten charge with the pellets to provide flexibility in the com-position of the final product; i.eO, to provide a composi-tion better adapted to stainless steel production. It has been found expedient in stainless steel production to ad-just the blend of waste materials and additions so that the pig produced in the melting furnace contains ~p to about 20~ nickel, about 2~ to about 30% chromium, and the - balance essentially iron.
The various distinct forms of metal-containing wastes suitable for conversion to metal values, such as stainless steel pig, include mill scale, furnace scale, high-grade gxit grinding swarf, furnace flue dusts, pickle

3~6 li~uor and process sludge. Mill scale is the oxide scale that forms on the suxface o~ hot metal and subsequently breaks away during the deformation imposed b~ hot~working operations. ~urnace scale is very similar to mill scale, it forms during high temperature heating of ingots, billets and slabs in preparation for hot working. Dry grinding oper-ations which are used to surface condition billets, e.g~, by removing seams and smoothing defects, produce a was~e material known in the industry as high grade grit. ~urnace flue dusts include the dust collected from simple dust-catchers located immediately adjacent to steel melting furnaces as well as the dust removed from primary and secondary wet and dry cleaners including bag ~ilters and electrostatic precipitators~ To fully remove scale formed during hot rolling operations and to clean the surface of cold-rolled stainless steel, an acid pickling operation may be employed. The pickling solu-tion after use is termed spent pickle liquor and containsmetal ions as well as variable amounts of residual acid. The used pickle liquor poses a difficult disposal proble~. Still another form of waste is process sludge. This is the precipitate collected from process water treatment.
Typical process sludges can contain about 3% Ni, 8% Cr, 30~ Fe, 7% C, 7~ CaO and 4~ SiO2. Grinding swarf is produced in finishing operations employed for sheet and strip products and also during centerless grinding. Usually belt grinding equipment is used with oil or oil-water emulsions as cool-ants. This resulting waste is an agglomeration of fine elongated metal particles interwoven with grinding media debris and soaked in coolant. Due to i~s low bulk density this valuable material is difficult to remelt in steel making ~31~6 furnaces. In addition the containe2 oi~ content produces large volumes of smoky fumes on heating that cannGt be treated in normal steel making melt shop pollution control equipment.
It is essential to the present invention that the types and grades of waste material be selected so as to produce a pellet with high strength and resistance to im~
- pact and to make advantageous use of the components of the waste materials. As a preliminary step, the waste materials are pxeferably screened to remove excessively large pieces of waste, i.e., those larger than about 2.54 cm diameter.
Oversize pieces are crushed and rescreened. Solid pieces of metal are removed and added directly to the melting furnace. The reductant which may be any carbon supplying material that is capable of reacting with said waste material and capable of providing a reducing atmosphere, e.g., a low-cost anthracite, is added in crushed form.
It is essential that the quantity of the material selected from the group consisting of furnace flue dust and process sludge ~e present in an amouni of at least about 20~ by weight, to produce the required strength and impact resistance in the pellets since it is one of the most important features of the present invention to elim-inate the use of any binder material in the pellets formed thereby avoiding one of the most undersirable drawbacks of the prior art waste recovery processes. Mo more than about 85%, by weight, of these constituents should be present to provide an economically useful pellet. The waste materials consisting of mill scale, furnace scale, and high-grade grit provide the balance Gf the dry charge in an amount ranging` from about 10~ to about 75~, by weight. ~or ex-ample, a mixture of 10% anthracite, 60~ mill scale and 30%

i6 furnace flue dust can be used in a blend. It has been found that grinding swarf can be added to the mixtures up to a level of about 20% by weight of all other constituents. At this level, thle oil contained in the swarf has only a modest effect on lowering pellet strength.
The presence of flue dust and/or process sludge is essential in order to provide fine material for void filling and to promote agglomeration during pelletization.
Use of flue dust is also important from a commercial standpoint as it is a rich waste posing a difficult and costly disposal problem. In order to satisfy these needs, the invention has incorporated a novel use for another di~ficult to dispose of waste, namely pickle liquor.
A feature of the invention is the lack of need to add binder materials to the blended waste mixture in order to produce pellets of sufficient strength for further pro-cessing. It has been found that pellet strength can be increased by the use of pickle liquor substituted for all ~o or part of the water added during the blending operation.
~his approach has a number of benefits in addition to im-proving pellet strength; another difficult t~ dispose of waste is employed and the metals contained in the pickle liquor (e.g. Fe, Ni, Cr and Mo) are recovered.
It has been found that when the normal blend of waste material (as described above) containing flue dust of typical CaO content (about 8~) is pelletized with use of pickle liquor as part or all of the moisture an im-provement in pellet strength is obtained over those made 3~ with water as the only source of r.loisture. Flue dusts with ~1~3~
higher CaO contents (up to 50~) can on occasion b~ pro-duced by the steelmaker par-ticu]arly if a high lime slag practice is being employed for enhanceci steel desulfur:i-zation. Such high CaO flue dus-ts can be employed as part of the blended wastes and good quality pellets can be produced. However, said pellets rapidly lose strength after short storage times to the polnt where their strength is effectively zero. The failure cause had been identified - to be the taking-up of pellet moisture by reaction with CaO to ~orm slaked lime (Ca(OH)2). Thus the moisture essential to pellet strength is removed. The situation is further aggravated by the almost double volume expansion in the transformation of CaO to Ca(OH) 2 which causes a build up of pressure within the already weakened pellet resulting in fracture and decrepitation.
. .
The addition of pickle liquor during -the blending operation overcomes this problem by reacting CaO with the q residual acid content of the pickle li~uor to produce dense crystaline calcium salts. Salts of the valuable metals contained in the pickle liquor also precipitate at this time thus incorporating these metals in the pellet ~for recovery in the subsequent processing steps. The xesidual acid level in the pickle liquor can be variable and the amount of pickle liquor added to the blend can vary without - appreciably affecting pellet strength. This is because it - is not necessary to transform all the CaO to calcium salts;
A coating of calcium salt around a predominantely CaO particle effectively seals and blocks the CaQ from reaction wi~h water to form slaked lime. We have found that addition of pickle liquor of up to about 20~ by 7eight of the blena is effective if 3~6~

high CaO flue dust (~35% CaO) is present in the blend.

The amount of spent pickle li~uor can be reduced to about 5%
if low CaO flue dust (<~5% CaO) is use~ although the higher pickle liquor level can be maintained without deleterious effects.
The various waste forms are generally blended with a small amount of water and/or pickle li~uor to facilitate the pelletizing operation. Up to about 20 water, e.g., 8%, by weight of charge is added during blending in a conventional blending device such as a pug mill.
The pellets are formed by any suitable means, e.g., on a disc pelletizer. In addition to the water and at times the pickle liquor added during blending, additional water is added during pelletization to pro-vide~a total moisture content of from about 5% to about 20% by weight of dry charge wqight, and preferably from about 8~ or 10~ to about 13~ or 15%. After the pelle~s have been formed on the pelletizer, they have sufficient green s rength for further handling. Pellets from about one to about four centimeters diameter are preferred for roasting and melting operations.
The reductant blended with the waste materials can be any carbonaceous substance as long as it is capable of reaction with the waste materials a~d is capable of pro-viding a reducing atmosphere for said waste materials.
Anthracite coal and petroleum coke are examples of rela-tively inexpensive substances that are particularly effec-tive for performing the reduction step. The quantity of reductant added should be from about 5~ to about 30~, by 3~66 weight of the dry charge, and preferably from about 8%
to about 20~. Reduction is incomplete and not as satis-factory in pellets containing less than about 5~ reductant.
More than about 30~ reductant provides little added benefit.
The reductant should be in a fine crushed form, e.g., not greater than 6mm. It is preferred that the particles have no dimension larger than about 4mm.
It can be seen from the reaction below, that the carbonaceous reduction material, in fact, does not serve as a binding material for the formation of the pellets but does serve as a medium for supplying the necessary reducing a~mosphere for the recovery of the metals present in the waste materials. In addition to direct reaction with the wastes the carbon present in the reduction material reacts with the ambient carbon dioxide and the water to form carbon monoxide which in turn reacts with the metal oxide present in the waste material. The reaction is as follows C02+C~H 2 C0 H20+C~ C0+ H2 CO*M0 ~ C~ 2 + M
In the above reactions M is a metal.
The carbon dioxide andthe water shown in the above reactions are evolved from the combustions taking place as a result of the heat required for maintaining roasting temperatures.

Reduction roasting prior to smelting serves to substantially lower the levels of volatile elements such as sulfur, lead, zinc, etc., at an early stage in the pro-cess so that these elements can be more easily removed and recovered by pollution control equipment. The early re-moval of such elements provides for advantageous, cleaner conditions during the melting operation with resultant im-proved cleanliness of the final product. By providing efficient atmosphere control, the reduction roast increases the effectiveness of the carbon contained within the pellets and consequently the overall process efficiency.
During roasting, the volume of the pellets decreases substantially, by as much as about 40%, which lessens melt-ing time considerably. Decreased bulk and increased thermal conductivity leads to rapid and less expensive melting which is combined with advantageous use of the electric-arc furnace for melting.
In additlon to the presence of the reducing atmo-sphere supplied to the pellets by the carbonaceous reducing ? material, the pellets should be subjected to a neutral, slightly reducing or preferably a moderately reducing atmo-sphere, e.g., an atmosphere containing 30% CO and 70% Co2, in the reduction unit.
In one ~referred embodiment of this invention, pellets are gradually heated to a temperature between about 1000C to 1300~C in a reducing atmosphere. This may be accomplished as described hereinafter by passing stainless steel wire mesh boats containing green pellets through a mu~fle furnace.

~3~
A most advantageous variation of this process which is particularly adaptable ~o production conditions is contemplated in which a shaft preheater is used in combination with a rotary hearth furnace. The shaft pre-heater is a larger diameter cylindrical vessel which can be constructed from refractory-brick lined steel. The unit has a slot at its base which can be opened and closed to control the flow of pellets into the rotary hearth furnace. The use of a shaft preheater reduces the overall hearth area requirements for heating and reduction as well as providing a method for waste heat recuperation. The shaft preheater is not an essential feature of the process.
Preheating of the pellets can be done on the hearth and economic objectives met by heat recuperation from the furnace off-gases.
The shaft preheater is positioned atop the rotary hearth furnace and a portion, roughly half, of the off-gases from the rotary hearth furnace pass through the shaft preheater. Green pellets are charged into the shaft preheater where they encounter the reducing off-gas from the rotary hearth ~urnace which drys, heats and partially reduces the metallic values of the pellets.
Temperatures of about 400C to about 900C, e.g., 800C, can be achieved in the shaft preheater. Subsequently, the pellets are further reduced during heating to tem-peratures of abou~ 600C to 1300C, e.g., 1100C, in the rotary hearth furnace. Gas flow within the rotary hearth furnace is opposite to the direction of pellet travel. Substantially, all of the nickel and iron,and up to about half of the chromium can be reduced to the metallic state at temperatures within the aforementioned range. The non-reduced chromium is completely reduced in the arc furnace; however, with ideal conditions and elevated temper-3~G
atures all of the chromium may be reduced in the rotary hearth.
In another preferred embodiment of the invention, after passing through the shaft preheater, pellets are heated to temperatures of about 600C to about 800~C in the xotary hearth furnace for purposes of economy. At these temperatures, only the iron and nickel values of the wastes are reduced, whereas the chromium remains in the oxide state. In this embodiment, chromium oxide is reduced to metallic form within the melting furnace.

When a rotary hearth furnace is used for the re-duction step, it is possible to introduce still another type of stainless steel waste. A waste material known as oily grindings can be added near the product discharge section of the rotary furnace. The temperature in this section of the rotary furnace should be in excess of 600~C to avoid smoke formation.

, Oily grindings are produced during operations such as the wet-surface grinding of rolled shapes. This type of waste is not favored fQrpelletizing due to its excessive oiliness; however, its residual hydrocarbon content is used advantageously as a fuel source.
The process of this invention is preferably per-formed on a continuous or semi-continuous basis in order to retain the sensible heat value of the pellets. Where pellets are charged continuously to the melting furnace, e.g., via a launder, molten metal and gangue are generally tapped from the melting furnace with regular frequency. In another and pre-ferred embodiment, the reduced pellets can be ~ransferred from 3~

the reduction unit to an insulated product bin and then into a sealed refractory-lined container. The container advanta-yeously provides a means for maintaining reduction and melting units on the same level. The container retains the sensible heat and prevents reoxidation of the pellets by contact with the atmosphere. In this embodiment, the reduced pellets are collected in a quantity suitable for charging to the meltin~
furnace which can be operated on a continuous or a batch basis as desired.
The reduced pellets should be melted in an electric arc melting furnace utilizing graphite electro~es. ~hile other types of melting units might possibly be employed, the conventional electric-arc ~urnace is greatly preferred and considerably more advantageous commercially. For example, in connection with furnaces of the induction type, the reduced pellets do not have sufficient electrical conductiv;ty as required in induction melting. Moxeover, this unit ~oes not appear particularly useful unless a graphite lining (which acts as a susceptor) is used. And even with a ~raphite lining, induction melting is not as efficient as electric-arc melting because of slagging difficulties, electrical losscs, etc.
An electric-arc melting operation is started with a metal charge, or heel, which forms the initial molten pool beneath the electric arc. This heel can be formed by meltin~
a small charge of scrap metal or by leaving behind a molten pool from a prior melt~
The carbon content of the initial molten pool and the carbon content of the reduced pellets should be sufficien~
to provide a carbon content of at least about 2~ in the molten ~ 6 ~

metal. This amount of ca~bon is ~enerally required to provide ad~itional chromium ~eduction during melt-down of the pellets and to prevent chromium oxidation within the molten metal.

The rate at which the charye is melted in the electric-arc furnace is largely a function of the size of tlle furnace and to some degree the reduced metallic content of the pelleLs. Generally, conditions are established so that a molten slag or gan~ue layer floats upon the surface of the molten ~etal pool. Pellets charged into the electric-arc furnace sin~ beneath the surface of the molten slag while un~ergoiny completion of the reduction xeaction and melting o the l~clletsA With proper adjustment of the slag basicity, as described previously, the pellets are pro~ected from oxida-tion since they sink beneath the surface of the slag and the slag is nonreactive with respect to the pellets. In a batch operation, sufficient time must be allowed to provide for settling or separation of the metal from the gangue.
The temperature of the furnace should be between about 1550C and 1700C. Temperatures below 1650~C can lead to solidification of the slag which is undesirable and excessive temperatures can cause breakdown of the refractory lining of the furnace as well as lead to excessive enerqy cost.
Following the settling period, the temperature of the slag and metal is generally lowered to about 1500~C to 1600C. This somewhat lower temperature aids in avoidînc3 unwanted oxidation o the molten metal durinc3 the pourin~
of pigs.

~3~

The pouring operation ~an ~e accomplished by tilt-inq thc electric-arc furnace, or tapping through tap holes, to first remov~ the slag layer which is subsequently dis-carded ald then pouring the rnolten rnetal fraction. The molten metal is preferably poured into molds on a continuous pig casting machine.
The reclaimed stainless steel can also be poured into an insulated container and transported to a nearby Ar~on~
Oxygen-Deoxidation unit for further processing. In such A~
; 10 AOD unit, the levels of carbon and sulEur as well as leve~s of various other harmful or tramp elements can be substantially lowered.
During the reduction operation as well as t:he melt--ing operation, a number of volatile elements, e.g., Zn an~l S, as well as dust must be prevented from entering the atmosphel-e.
This is accomplishea by the use of conventional dust collec-tion, wet scrubbing and electrostatic precipitator devices.
Substantial quantities of elements such as zinc may be recovere~
from these dusts and gases by well-known processing sequences.

For the purpose of giving those skilled in the art a better understanding of the invention and/or a better appreciation of the advantages of the invention, the follow-ing illustrative examples are given:

EX~IPLE I
A rotary mixer was used to blend a 900 kilogram charge consisting of 30~ of flue dust A (Table I), 90% mill scale B, 20~ mill scale C and 10% crushed anthracite. The fine dust and mill scale were screened through a 2.5 cm mesh and large metallics removed prior to introduction to the mixer.
The anthracite was screened to have particles no larger than 3 mm. The blendin~ ope~ation was carried out for a~out 20 ~3~6 minutes and the aim and fina:L compositions of three representative samples of the mixture are shown in Table II~

. I . ~3 .

O u~ o In P' C~ .~ o P~ C.~ ,. ..
o ~, .~ .~ C~
E~ o c~
.. ... ..
~-~ ~D el o U~ ~ C~ ~i .. ..... -cn ~ o .r~
Z N e~ N
.. .~
~0 N ~ N
~ O O C~
8 ~ C3 r~
~ r cn r;
~ ~ c~
v ~ .
~ o o o ~ cn .r~ ~ co r~ co ~ c~
.r~ o o o ~q o ~
~ t) N O
V U~ O C~
..
~ o ~o O, O O
r~ r~
el~ O C~
O O O
~ .. , - ... -V . r-l ~ r~ O
..
C~ ~ O
. ..
o N ~ ~

.. - ~ :
:: : m o : ~

a) a u~ u~
~- ~ ~, ., ~n : ~

: ~ .
.

3~

Pelletixation wa~ accomplished on a three~foot diameter pelletizing disc. The premixed powders were sprayed with about 10% water (by weigh-t). Pellets were readily formed having a mean diameter of about 1.2 centimeters, a size range of about 0.6 to about 2.5 centimeters ~eing acceptable and preferred for later processing. The green strength of the pellets was adequate for transfer to the reducing furnace, e.g., a 1.2 centimeter diameter pellet could support a load of about 5 kilograms without crushing.
EXAMPLE II
Green pellets, allowed to air dr~v for one hour, were placed in stainless steel mesh boats and passed ~hrough a horizontal electrical-resistance heated muffle furnace having a reducing atmosphere to simulate trea-tment i31 a com-bination vertical-shaft/rotary-hearth furnace. The furnace had a 18 cm by lg cm muffle cross section. The fllxnace atmo-~here was 30~ carbon monoxide plus 70% carbon dioxid~ ~lowing ~t the rate of 1.3 cuhic meters per hour (3.5 cm per millute vcloci~y) through the 0~16 cubic meter furnacc. Ilame-cllrtain doors ~erc used at both ~nds of the muffle furnacc to prevent oxidation of the pellets by the atmosphere. ~he ovexall lensth of the furnace was 5.2 meters with the last 1.~ meter water jacketed and used as a cooling zone so that pellets could be removed from the protective reducing atmospherc with-out reoxi~izing.
I~uring heating in the mu~le furnacc, a 2.5 cm dec~
1.~yer of ~cllets required about 25 minutes to achicve lO90~C.
'~hc ~ellcts remained in the hot zone of the furnace at a temperature in excess of 1090C ~or about 20 minutes. A
maximum temperature of 1180~C was attained during passage through the furnace.

.

~33L~6 o o o V V
oo o N N
O O O
.
¢1 O o .
,CI ¦ NO ~
U)O O O

ZU7t~CO
N ~N
11~Ln d U)' -~ N`D
.~~0N NH
~ . . .
C I 00 ~t ~
. . .
_~ O

' ¦ ~~, N
C~ ~ N ~ Il~
E~ . . .
~rl ¦ 1~ N C~ ~
u.l E-~ I o ~ o o ZH 1 N ~ 1 U.l ¢ ~ U~ N
~ . . .
C~
H ~--~1 ~ 1~ ' t~) H ~~ I H 0 N ~) C¢ C~l cdl ~
E-- ~ N ~ ~1 ~
O I ~
H ~ I N N
CJ~
~ ~ ~ ~ U~
¢ I ~ ~0 ~ ~
~ H H H N
o l 1~ r~ o u~
:~:1 o o ~, ~"

0~ ~ cn a u~
1~ N ~ ~

~D ~ ~ oO oO oO o\
Z ¦ N ~ ~ N
N ~D

a ~ .
N

~!

3~66 Followin~ the reductioh step, th2 pellets contained a~out ~. iron, 11.3~ chromium and 2.6~ nic~e1 in elcmc~lltal Eorm. ~rhcsc values reprcsent reductions of about 84% f~r iron, 12~ for chromium and 9S~ for nickel. T~ble III sho~
thc cc)ml)osition of the pellets followinq the rcduction step and in addition, sho~J~ that the content of undcsirable elements such as lead and tin is substantially lowered durin~ this portion of the process.
~ TABL~ III
Compositio_ of Pellets ~fter Reduction at 11~0C
Composition in Weight Percent : ~e : Cr : Ni :Al : Si :Mq ~iln :Ca : Pb : Sn Reduced ~c~lets:48.8:ll.3:2.86:l.3:2.7n:2.3:3.7:3.9:0.0~4:~0.()05 _ _ _ _ _ _ _ _ . _ EXAMPLE III
About 270 ky of the aforedescribed reauced pellets were melted in an electric-arc furnace for the purpose of:
~i) completing the reduction reaction, tii) melting the pellets, (iii) separating metal and gangue and ~iv3 providiny solidiied pigs o~ reclaimed stainless steel.
~0 An initial charqe of 180 k~ of pi~ iron containi.nc~
about 3.6% carbon was melted in an electric arc furnace.
~ollo~ing meltin~, about 2.3 k~ of f~rro-silicon (containin~
75Y. silicon) was addcd to maintain the c~rbon content of thc charge.
About 50 minutes were required to melt the cast iXOll and achieve a temperature of lS00C at which time pellets and limestone were introduced. Pellets were added at the rate of 2.7 kg every 2 minutes. To insure a favorable ratio of 3~

~ 'a~ ;J())/SiO2 of ~rom 0.8 to 1.8, a~o~lt 0.45 k~ of limt~st:one w~s ~d~le~l with each pellet charge. The operatiny,temperature of the electric arc furnace was maintained between about 165C) alld l7onoc~ This temperature range ~as achieved about one hour after start-up. After 3 hours of operation in this manner, 272 kg of pellet and 25 kg of limestone were consu~ed.
The furnace ~as mainta'ined at 1650-1700C for an additional 1/2 hnur to complete the reductio;n, melting, and separat~on reactions. Irhc tcmperature of the furnace was then lowcred lD to 1580~C and the slag tapped. The reclaimed metal was }~oured into cast iron ingot molds to produce ~i~s ~eighin~
about 20 pounds each.
The composition o~ the reclaimed metal ~nd slag shown in Table IV during the meltin~ operation and aftex separation of the slag and pouring. A materials balance ior this electric-arc furnace melt showed that about 99~. of the nick~, 9r~.8~ of the chromi~m and 95.8~ of the iron were r~coverecl during the meltinc~ process. Only 0.04~j nickel, 1.59~. chromium and 6.8~ lxon were retained in the discarded 2 D s ~ a~.
Reclaimed pigs such as those produced in this example and containing 9.1% chromium, 2.44~ nickel, balance iron are well suited for prcparation of conventional stain-less steels. Although the 2.95~ carbon content at first glance appears high, this level of carbon is suitable in pig used for supplemental additions ~o an electric-arc furnace and is particularly useful in the Argon-Oxygen-Deoxidation process for refin~ng of stainless steel, e.g., where high-carbon ferro-chromium (6-9% carbon) is routinely used.

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, 3~t~6 F.XA-r~P-~E-Iv ~ blend was made up containiny ~2.8~ flue dust (containing 32P~ CaO) 28.8% mill scale 1~.0~ swarf and 1~.3% crushed coal as the reduction atmosphere suppl~iny material. To this was added 10~; by weight of pickle liquor containiny residual nitric and hydrofluoric acids. Pellets were made on a pelletizing disc with water added to briny the total water plus pickle liquor content to :L~. Two hours after production, the peLlets had a crushing strength of about 20 lbs.

Similar pellets were produced from the same mixture but with water being the only source of moisture. Pellet crushing strength measured was about 10 Ibs. immediately after pellet formation but was so low after 2 hours stoxage as to be unmeasurable. The pellets wer~ jwollen and d:isintegrated upon touch.
, EXAMPLE V

- A blend with a composition similar -to that shown in Example IV was made up but with flue dust containin~ 15~

CaO instead of 32%. Two lots of pellets were prepared from - this mixture in the manner prescribed in Example IV. One lot had 10% pickle liquor added and the other lo-t was made .
up with water as the only source of moisture. Three hours after pelletization the pickle liquor containing pellets had crushing strength of~about 18 lbs. and the pickle liquox free pellets had crushing strengths of about 10 lbs. After reduction under rotary hearth furnace condi-tions at 2200F
the analysis of both lots of pellets were essentially identi-cal. This indicates that the calcium compounds formed by reaction with the pickle liquor decomposed during the thermal treatment and are not carried forward to the melting stage of the process, 3~
EXAMPLE VI
.
A mixture consisting of 40% flue dust, 21 ~ mill scale, 17% oily swarf, 6~ high grade (metal billet)grit and 1~% crushed coal was blended at a rate of 10,000 lbs. per hour in a pug mill. Moisture was added in the form of pickle liquor at the rate of 1 gal. per minute. The mixture was pelletized on a 12 ft. diameter pelletizing disc at which point water was added to raise the total moisture to 12%.
The pellets were then transferred to a rotary hearth furnace and heated to a temperature of 1100C for a total residence time of 25 minutes.
Pellets were discharged from the rotary hearth furnace with 95~ of the nickel and iron content reduced to the metallic state. Reduced pellets were added to an arc furnace via a refractory lined transfer car. Following melt-ing and chromium reduction in the arc furnace the metal tapped from the furnace contained 10.22% Ni 20.4% Cr 0.8~`Mo 3O72 C
<0.005~ Pb <0.005% Zn 2D The temperature was 1600C at tapping.
The slag phase tapped from this furnace contained the following D.25~ Ni 1.3~ Cr, etc.
~he basicity as measured by the ratio of CaO+M~ O~SiO2+Al 2 was 1 6. The slag temperature was 1525C.
Although the present invention has been described in conjunction with preferred embodiments, it is to be under-stood that modific:ations and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

. . _ . . _

Claims (21)

PC-2?B/CAN
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for recovering nickel and other alloying metal values from waste comprising: blending a waste material containing at least one material selected from the group con-sisting of mill scale, furnace scale, and metal billet grind-ing grit, said waste material characterized by a particle size up to about 2.5 cm diameter, with a reducing atmosphere supplying carbonaceous reductant, a liquid selected from the group consisting of water, pickle liquor and a mixture of water and pickle liquor and at least one material selected from the group consisting of furnace flue dusts, sludge and metal containing process-water sludge to form a blended feed material; pelletizing said blended feed material to form strongly bound pellets said formed pellets maintaining their integral shape without the need for additional bonding material; heating said pellets in the generated substantially oxygen free reducing atmosphere for the purpose of reducing waste material metal oxides in said pellets, thereby forming a metal-containing pellet; and thereafter melting said metal-containing pellet to separate and recover metal values.

2. A process as defined in claim 1 wherein said strongly bound pellets contain at least one material selected from the group consisting of furnace flue dust, sludge and metal con-taining process water sludge present in an amount of, in weight percent, of from about 20% to about 85%.

3. A process as defined in claim 1 wherein said carbonaceous reductant is present in an amount from about 5%
to about 30%, by weight, of said blended feed material.

4. A process as defined in claim 3 wherein said carbonaceous reductant is present in an amount from 10% to about 20%.

5. A process as defined in claim 1 wherein said carbonaceous reductant is coal.

6. A process as defined in claim 1 wherein said carbonaceous reductant is petroleum coke.

7. A process as defined in claim 1 wherein said liquid is water.

8. A process as defined in claim 1 wherein said liquid is pickle liquor.

9. A process as defined in claim 1 wherein said liquid is a mixture of water and pickle liquor.

10. A process as defined in claim 1 wherein said strongly bound pellets are heated to a temperature of from about 400°C. to about 1300°C. in said reducing atmosphere.

11. A process as defined in claim 9 wherein said pellets are heated to a temperature of at least about 600°C.

12. A process as defined in claim 1 wherein said liquid is added in an amount of about 5% to about 20%, by weight of said blended feed material.

13. A process as defined in claim 1 wherein one or more of burnt lime, limestone, magnesia, steelmaking slag and chromium-rich substances are added during said melting step with said metal-containing pellets.

14. A process as defined in claim 1 wherein said metal value contains, in weight percent, from about 2% to about 30% chromium, up to about 20% nickel and the balance essentially iron.

15. A process as defined in claim 1 wherein said pellets are from about one to about four centimeters in diameter.

16. A process as defined in claim 1 wherein said waste material is a stainless steel making waste material.

17. A process for recovering nickel and other alloying metal values from stainless steel manufacturing wastes com-prising; blending a waste material containing at least one material selected from the group consisting of mill scale, furnace scale, and metal billet grinding grit with a sub-stantially oxygen free reducing atmosphere supplying carbon-aceous reductant, a liquid selected from the group consisting of water, pickle liquor and a mixture of water and pickle liquor, and at least one material selected from the group consisting of furnace flue dusts, sludge, and metal contain-ing process-water sludge to form a blended feed material;
pelletizing said blended feed material to form strongly bound pellets said formed pellets maintaining their integral shape without the need for additional bonding material;
partially reducing said pelletized waste material by heating said pellets to temperatures of from about 400°C to about 900°C in a substantially oxygen free reducing atmosphere and continuing the heating to the complete reduction of said pellets to the metallic state at a temperature of from about 600°C to about 1300°C, said reducing atmosphere being supplied by said carbonaceous material; and thereafter melting said metal-containing pellet to separate and recover the metal values.

18. A process as defined in claim 17 wherein the partial reduction of said strongly bound pellets in the reducing atmosphere is conducted in a shaft preheater.

19. A process as defined in claim 17 wherein said liquid is water.

20. A process as defined in claim 17 wherein said liquid is pickle liquor.

21. A process as defined in claim 17 wherein said liquid is a mixture of water and pickle liquor.