3
Pigment Grade Iron Oxides RECOVERY FROM IRON-CONTAINING WASTE LIQUORS C. C. DEWITT, M. D. LIVINGOOD', AND K. G. MILLER Michigan State College, East Lansing, Mich.
A
CONTINUOUS pilot plant for the wet process chemical production of synthetic pigment grade iron oxide has been in production for some time, producing principally red and yellow oxides. This pilot plant has exhibited very marked advantages in ease of continuous, automatic operation, low labor requirements, and cleanness and other desirable properties of the colors produced. With relatively simple equipment and controls it has been possible to produce excellent red and yellow oxides as well as other intermediate shades of commercial importance. The raw materials for these operations have been those occurring in commercially used pickling operations. Both synthetic mixtures of the several iron salts occurring in pickling wastes and the pickling wastes themselves have been tested. The pilot plant is very compact and simple in construction. For many years the senior author has worked with both natural and synthetic iron oxides. From the beginning of this work it was apparent that, whatever the desired end use, the natural pigments were inconsistent in their properties. Through the years, the natural iron oxides have become either geographically remote or politically unavailable. This, coupled with the availability of large quantities of waste iron salt solutions, principally originating in the pickling of ferrous metal products, has indicated continuing research-on better methods of producing synthetic iron oxides from these materials. In 1947, government statistics show that the quantity of sulfuric acid waste pickle liquor from the steel industry is known to have been equivalent to a t least 200,000,000 gallons of 10% ferrous sulfate (25); many authorities agree that a t least five times this quantity of pickle liquor was produced, and only a small amount of these liquors were processed for recovery of the ferrous sulfate or other iron salts contained in them. Spent pickle liquor contains 5 t o 25% of ferrous sulfate (average 15%), 0 to 12%sulfuric acid (average 5 % ) , and minor quantities of organic or inorganic salts depending on the pickling process used and whether the operation is batch or continuous. Pickle liquor may contain instead of ferrous sulfate, ferrous or ferric chloride and other iron salts depending on the use of pickling processes employing hydrochloric or mixed acids. No reliable estimate is available of the ferrous salts available in hydrochloric or mixed acid pickling wastes. Three general methods for synthesizing iron oxides have been discussed by DeWitt and Livingood (4) in a comprehensive review of the literature and present art in producing synthetic iron oxides. Of these, chemical precipitation with oxidation either before or I
Present address, 136 Atlas Drive, Collins Park, New Castle, Del.
after precipitation, followed by concurrent or subsequent conversion to the oxide has exhibited great advantages over the other methods. It has been shown by many investigators (4,6-9, 14, 16, 19, 22, 24) to be the only method capable of producing wide color variations. It is adaptable to utilization of by-products from other industries as raw materials or iron source and for precipitant or oxidant. The chemical process has also shown itself peculiarly adaptable t o the production of stable and reproducible oxide materials which do not require further grinding or conditioning for pigment use. The process based on the chemical method has been studied by these investigators and others in great detail. Processes involving precipitation as sulfate, carbonate, ferrite, or hydroxide with subsequent oxidation and conversion to oxide; primary oxidation followed by precipitation and conversion; partial oxidation and precipitation, then complete precipitation followed by further oxidation and conversion; and methods whereby the oxidation, precipitation, and conversion are carried on practically simultaneously, either from metallic iron or iron salts, have been recorded. Operating conditions have varied widely, and oxidation iates have been singled out for study. The rate of oxidation (6, 7 , 16, f?, 19) controls to some extent (depending on other conditions) the color and the particle size of the pigment produced. Certainly none of the processes published t o date attempts to combine increased reaction rates with continuous operation for ' t h e most efficiefi production. All plants repoited have been either batch or semibatch. Superatmospheric heat and pressure have been used since the initialvpatent of Marks ( I S ) . Moderate heating of precipitated reaction masseg generally produces yellow or brown pigments, depending on other conditions (6, 7 , 20). Stronger heating has been recorded as producing black or red pigments (1, 6,20,86) Catalysts to control the rate of oxidation or conversion in the wet phase have been proposed : Manganese dioxide has been used as a catalyst-oxidant (21) ; trivalent and tetravalent salts have been employed by several investigators (10, 11); boric acid or its salts (14, acetic acid or sodium acetate (18) have also been used; and iron rust has been proposed (25, 24). The presence of metallic iron is specified by several workers as a negative or positive catalyst (5,12, 16-17'). The consistency of the solution has nleo been used to control oxidation rates (16, 17). The p H of the reaction mixture does not seem t o have leceived much attention. Ayers (Z), Elzi (6), and Ryan and Sanders (19) have specified conditions which partially or possibly control pH; however, little general interest has been shown 61'3
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 3
EXPERIMENTAL WORK
Pilot Plant for lied Oxide Circiilating p u m p in foregroiind; holding druin and heat rxchangei at right
in controlling pIl provided an e1npiric::iI set, of conditioiis gave the desired result,s. According t80Taffee (W2)it geiicralieed pattern lor wet product,ion of varioua iron oxidcs appears to bc:
A small batch pilot plant vas constructed using industrial type equipment which could be used to st,udy the precipitation and conversion steps in the gcneral production of oxide pigments. This plant consisted of a heat exchanger, designed to handle suspensions of solids n-ithout undue fouling and viithout corrosion; a pump t,o circulate the hydrouidc-oxide suspension ihrough the heat exchanger and remainder of the system; a holding drum designed to xithstand pressure operation and of sufficient capacity to produce the desired t,iine-space relation; and a temperature control to hold t,he system tcniperature a t predetermined values. Pressure was controlled manually, and a separate tank ~t-asused for mixing and introducing solutions into the system. The heat exchanger a i d pump gave considerable trouble both individually and as a unit, before satisfactory designs were secured. I n practice the combination of high system pressure with large suct,ion to discharge pressure diffcrences and a hot corrosive solids-containing suspension played hob xith cont,act surfaces subject t o the suspension. In early trials t8hemating surfaces of several different kinds of gear or positive displacement pumps galled rapidly. In addition, stuffing boxes failed rapidly, and bearing seizure and shaft scoring were commonplace occurrences. Some pumps lasted for only 1.5 hours. These early trials indicated a need for a centrifugal pump xitl-i an excellent stuffing box which could be provided with water cooling and some sort of seal to keep the solids from entering the stuffing area. After a year's correspondence, two manufacturers agreed to provide a centrifugal pump TThich they would guarantee to handle alkaline or acid hydroxide slurries a t temperatures above 300" F. and system pressures of 125 pounds per square inch gage or more. The pump finally selected had water-cooled ball axial and thrust bearings as well as a deep, water-cooled stuffig box provided with a lantern ring. The impeller had a large wearing ring, and the shaft was provided with a wearing sleeve. This pump proved very satisfactory in service; the only stuffing box troubles occurred when the lantern ring was not kept full of sealant. Inspection of t,he liquid end a t intervals revealed little wear and little corrosion, even though the pump was inadvertently choked twice with settled solids. A
1. l'recipitation of a ferrous or frrrous-ferric hydroxide or other hydrogel 2. Oxidation of this hytlrogcl or t'hc original salt to a known ferrous-ferric content, 3. Conversion, nit'h or without a catalyst, of the hydrogel or original salt by heat and prcr~sure to the desired form of ferrousferric or ferric oxide
Ilewsrch oii thc 17 ct c*hemicalincthod ioi producing synthetic iron oxides has been conducted for some time by vaiious workers undei the direction of the senior author. These investigations x cre (xiried on first in laboratory equipment as small as 100-gram capacity and later in pressure vessels of &gallon capacity; a wide variety of pressurc and atmosphcric c.onditions were investigated. The small scale work indicated that colors from black through blue, purple, red, orange, and yellow iron oxides could be produced from the various iron salts containrd in pickle liquors and from thc pickle liquoib themselvw. Careful attention was paid to control of conditions so that clear-colored pigments could be made and reproduced t o color and particle si7e specifications. The small scale work indicated that p H as me11 as the precipitants, oxidants, temperatures, and ])~essuiesused had a profound effect on the physical properties and color of the pigments produced. Taffee (28) further substantiated these indications and also postulated that thepHshould lie of importance duiing all steps of a process pioducing synthetic iton oxitlcs
Figure 1. Batch Ked Iron Oxide Plant TI = Mixing tank (60-gallon drum) RB = Reactor HE1 = H e a t exchanger PI Centrifugal circulating pump T2 = Blowoff tank
-
Once the problem of the pump was settled, selection of a heat exchanger was not 60 difficult. -4heat exchanger of a large area and conimercially available design a t low cost was depired; an all-steel exchanger of the shell-and-tube type with four tube passes and U-tube construction was selected. This was operated with steam on the shell side and process suspension on the tube side; the tube bundle was approximately 6 feet long, and the inlet and outlet connections were ll/d-inch standard pipe thread. All system piping was of this size. A holding tank was made from '/&oh steel plate with ASNE dished ends, It pias provided with 11/2-inchI P S coiinections at
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INDUSTRIAL AND ENGINEERING CHEMISTRY
675
CONTINUOUS PILOT PLANT-RED OXIDES inlet and outlet (top and bottom) and with a series of I-inch sampling taps on a vertical line a t 6, 12, 24, and 36 inches from After the success of converting ferrous-ferric or ferric iron solutions t o desirable iron oxide pigments was established, i t was the bottom. The tank was approximately 72 inches tall and had decided to convert this plant to continuous operation. T o aca capacity of 100 gallons. complish this, a bellows-actuated differential air relay was inThis equipment is illustrated in Figure 1. It was so arranged that a charge of solution contained in the holding tank was circu*stalled on the holding tank with taps a t top and bottom, and the lated from the bottom opening through the circulating pumps, detected liquid level was exhibited on a proportional acting liquid level indicator-controller. This instrument controlled an airfrom which it passed through the heat exchanger and then through an overhead line back t o the top or inlet connection of the holding tank. A temperature-sensitive element and an ordinary thermometer were installed on the holding tank. Pressure gages were provided on the holding tank and at the pump outlet. Samplingcocks were installed on all the side outlets; on one of these, in addition, a compressed air line was connected. An additional sampling ~branch was arranged a t the pump discharge. The mixing tank was a standard 55-gallon drum; this, although i t required replacement relatively often, served satisfactorily. I t was provided with a bottom outlet, and a portable motor-driven u mixer with stainless steel shaft and propellers was PI used t o mix the solutions. The mixer performed satisfactorily; its stainless shaft was not attacked by either t h e alkaline or acid solutions t o which it was exposed. Solution was introduced t o a valved connection between the holding tank outlet and the pump suction. Dr. Temperature control was supplied by a bulbactuated, proportioning-type recorder-controller Figure 2. Continuous Red Iron Oxide Plant operating a n air diaphragm motored balanced port valve in the steam supply line t o the exchanger. TI Ironsolution and precipitation D R = Dryer tank F = Bag filter Ninety-pound was and little TB = p H adjusting solution tank A = p~ recorder-controller was experienced in controlling temperatures from TS = PH control and surge tank B = Charge temperature recorder-controller T4 = Blowoff tank C = Reactor temperature recorder-controller the maximum attainable (within 5' of the steam PI = Char e pump D = Reaotor liquid level recorder-controller temperature) down t o room temperature. The ~ ~ ~ ~ ~SI =~Iron salt f h $ ~ ~ entire system was insulated with standard magHE# = Recirculation heat exchanger 5 2 = Preoipitant R1 = Reactor SS = pH adjusting salt nesia insulation. C1,B = Centrifugals W = Water I n this equipment, the following factors were studied: operated diaphragm valve which was placed in t h e former sam1. Time required to convert a ferrous-ferric or ferric hydrogel pling line between the pump discharge and the heat exchanger int o the oxide let. Since in releasing the pressure large quantities of water vapor 2. Temperature reguirements were produced, the discharged material was led t o a disengaging 3. Color variations, other variations held constant 4. Effect on physical properties, such as particle size, ability drum which was vented t o the atmosphere with large diameter to mix with oil, drying characteristics, etc. pipe. This drum also functioned as a decanting barrel in concentrating the finished pigments. The following experimental procedure was followed for all the It was necessary t o find a charge pump that would continually batch runs: and accurately meter the desired amount of fresh feed-precipitated iron solution to the system. Again much trouble was en1. Iron salt was dissolved in a separate container in the desired concentration. countered in securing a pump that would remain volumetrically 2. The precipitating agent was dissolved in another conconstant and efficient. This requirement precluded the use of 8 tainer. centrifugal pump. After trials, a vane pump with hard carbon 3. The two solutions were mixed in the mixing drum and vanes and side plates, all other moving parts or liners being made made u p t o the desired volume. The p H was adjusted t o the specified value. of stainless steel, was found t o perform satisfactorily. This pump 4. The mixing drum was pumped out into the system. had a mechanical seal made up of a spring loaded carbon wear5 . With the circulating pump running, steam was turned into ing ring backed up by a neoprene seal. It was found necessary the heat exchanger. t o take only normal precautions in rigidly excluding all large 6. Samples were taken from the sampling drum every 15 minutes until tests indicated constant composition. No difference solid particles from the system; the finely divided iron precipibetween successive samples indicated completion at the first tates or oxides were handled without difficulty. sample. With the altered system, the routine was as follows: 1. Solutions were made up as before. Tables I and I1 show the results of typical tests on the batch 2. Sufficient solution was charged into the holding drum to plant. It is noteworthy that the best results were also secured raise the inventory to that desired for the run. with the shortest conversion times. The greater part of this work 3. Heating and circulation were begun, the temperature and was done with ferric salt solutions and red or brown oxides were pressure being predetermined. 4. When flow samples withdrawn from the system indicated produced; later work, although not so exhaustive, indicated that proper color and conversion had been attained, charging was blacks could be made as easily under similar conditions, t h e only begun using similar feed. This feed was preheated within a few variation being the ferrous-ferric ratio, the precipitating agents, degrees of the system temperature in a closed steam heated exand pH. changer inserted in the charging line. 9
$sl
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INDUSTRIAL AND ENGINEERING CHEMISTRY
676
TABLE I. TESTR C X S I N BATCH P L A K T R.EACTANTS
Color Dark brown
pII
Light red Red hIcdiuiii rcd
11 10 10
10
l'ressurf!. Lb./S(I. Inch Gagc 85 $1 4 82
85
~
fynp., 312
Time, 11in 65
320 310 320
2: 25
05
TVITII \'ARloUs
Reactants I-cP(QO.1)3,1~1.80, NaOH I,'eCls, Ca(O1I)r l'ez(S0~)s. NaOII FCC13, SnOH
TABLE 11. TESTlZuxs IS BATCHPLAST-FCC~,,N.1011 REACTANTS l'res-
Brown Red Red Red Clearred
B
7 8 9 10
76 00 100 85 65
307 300 320 320 270
10.5 ')0 RO 23 I .j
5. Continuous testing wab iegarded as beginning nlien the original contents of the system had been cbompletely replaced. If under these conditions the desircd color r a s maintained, the run Fas deemed successful.
Vol. 44, No. 3
in the slow oxidation with air of ferrous iron solutions with no iron or ferric iron present. Success of t,he 1ai)oratory scale tests and of t,he continuous pilot plant for red oxides indicated the desirability of constructing and testing directly a pilot plant for conttinuous production of yellow oxides 1)y the two iiiet,ho& out,linetl. A reactor was constructed from a length of 8-inch steel pipe, 130inches long, which was provided with I 50-pound screlved flanges at each end. End closures were made from 150-pound bl:tnk cast-iron flangcs which were drilled and tapped to provide a lja-iiich outlet and a 3/4-i11chinlet :it the top arid bottom. In addition, two l/n-inch couplings were wclded in line on t,he side of the reactor 53 inches al)ai%. On these couplings a bellows-actuated differential air relay, acting :is a liquid ievel detecting device, was mounted. The level detected by this element w i s shown on a liquid level indicator-contioller of t h r proportional type, which operated an nir-actuated (hiphrsgni valve. The entire reactor x i s lined with three coats of a vinyl plastic corrosion resiting material which was' cured a t 250" F. The bottom of the reactor \vas provided with a falsc k ~ t t o l i i which could he used t o hold a charge of steel or iron scrap. The false bottom was perforated and raised about 4 inches above the bottom flange by spacera. .A mixing tank of 50-gallon capacit.y
lypical runs in continuous opei,ntion :ire prosented in Table 111. These runs were again principally concerned ~vitlithe produetion of red oxides, although some tests were made and examples arc included of the production of black oxidc from ferrous-ferric solutions. These runs were, surprisingly enough, even more satisfactory than batch runs under the same conditions. In both batch and continuous runs under optimum conditions, the finished pigment was clear in color and in good yield; the mother liquor from the pigment. contained less than 20 p.p.m. of iron. Tho pigment was rcadily separable from the mother liquor by scdimentation; set,tling rates in free sedimentation were as high as 4.9 feet per hour. Thc settled particles were discovered by microscopic esaiiiiiiation a t I250 diameters to be agglomerates of alpha-ferric oxide (goethite) particles. Filar micrometer eyepiece measurements indicated t>hatthese particles were no larger than 1.5 microns, wit>h the principal Figure 3. Continuous Yellow Iron Oxide Plant number betvieen 0.5 and 1.O micron and many just visible particles below 0.5 Inicron. Doubtless ~6 = iron solution and precil,itation tank C I , ~= Centrifugals there are many particles smaller than 0.1 micron 2'6 = p H adjusting solution Dr = Dryer F = Bag filter present; the size of an individual goethite crvstnl T7 = pII adjusting and surgc tank A = Charge temperature recorderis said to be roughly 100 X 1000 A., and the ~ ~ ~ $ ~ ~ ~ a a ; k e x c i , a n g e r controller visihle particles are probably the bundles of crysI'S = Charge p u m p B = Liquid level recorder controller tals reported by Fricke and If-eitbrecht ( 9 ) . The R2 = Reactor iV = Water individual particles arc transparent to incident, light. They have exceedingly high tinting strength when diluted with titanium dioxide; they rub up satisfactorily provided \Tit11 a portable motor-driven mixer with stainless steel wit,h drying oils and have a high oil absorption value. Dried shaft and propellers was installed for preparing the solutions. films of these oxides in oil arc homogeneous and opaqucb. The precipitated solutions pnssed from this tank through ai1 80mesh strainer to a vane-type pump which charged the solution CONTINUOUS I n o r PLAKT-YELLOW OXIDES into the system against pressure. The solution entered the rewKarlier xork done under the direction of the senior aut,hor had tor at the top '/,-inch fitting after passing through :t singlcindicated that desirable yellow oxides could be produced by variations of the two generally TABLE 111. CONTINUOUS PRODUCTION OF IRON OXIDEPIGM used methods. The first of these consists in the simulPressure, Induction Tzmp., Lb./Sq. Period, Run Pigment PH, PH, F Inch Min. ltcactalils taneous oxidation and solution No. Color Inlet Product iZeC11.VnOlI of iron from a bed of thin iron 2ga Red: settles easily 13.0 12.5 320 104 60 12.5 320 126 15 01 Red; settleseasily 12.5 pieces submerged in a ferrous 13.5 320 137 40 13.5 30 Black 8.0 325 130 27 31 Brown-black 13.5 salt solution which is aerated. FeC13 , S a 0 1 1 12.0 11.0 310 125 40 Red This may be done a t tempera4 R u n 29 had some sodium oarbonate in the NaOII; when NazCOs is present a longer induction prriod is rcqriircd tures from atmospheric t o b u t the subsequent conversion is a t about tllc saine rate. 60° C. The second c o n k t s
g%
z
March 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
677
pass steam heated shell-and-tube preheater of all-iron construction. The temperature of the system was controlled by a vapor pressure thermometer and an air-operated recorder-controller which controlled a diaphragm air-actuated valve in the steam line. Liquid passed downward through the reactor and out through the valve controlled by the liquid level controllcr t o a 50-gallon receiving drum. A line was provided from the receiving drum t o the vane pump suction so that solution which had passed through the reactor could be recirculated; this line was likewise protected by a n SO-mesh strainer. High pressure air or other gases were introduced through the other bottom opening and passed upward through the reactor. A Cash pressure relief valve was installed on the top outlet; this valve was set t o the desired pressure for each run and was used to exhaust waste gases. The general scheme of operation was: 1. Steel scrap was placed in the reactor for those runs in which free iron was required. 2. An appropriate solution of ferrous salt was then made up in the mixing tank with whatever additives were under test. 3. Sufficient of this solution was pumped into the reactor t o fill it with 45 to 50 inches of hot liquid. 4. The feed was then shut off, and air or other oxidizing gas was introduced a t the pressure under test; the relief valve was set to a pressure less than this in order t o continuously purge waste gas. 5. An induction period was allowed for conversion of most of the ferrous salt to ferrous oxide hydrate; continuous sampling a t the liquid outlet indicated when this had taken place. 6. At this time, continuous charging of feed was begun with the system arranged for straight-through or partial recirculation operation. 7. A run was considered satisfactory if a coior was good and constant after the contents of the reactor had been renewed a t least twice. Results of typical runs with this unit are given in abstract Reaction Vessel for Yellow Oxide form in Table IV. Using ordinary air as the oxidant, reasonably Automatically controlled valve in exit line in foreground: bright yellows were secured with operation at retention times of preheater for circuit at right: feed tank in background 10 t o 20 minutes. Recirculation of the suspensions a t a 1:l recirculation ratio improves the brilliance of the yellow. Higher temperatures seem t o give darker yellows, although no definite red iron oxide and of a plant with a similar capacity for browns are evident a t the throughput rates observed. Batchproducing yellow oxide. These two plants were designed so wise aeration in the middle of one run darkened the yellow conthat they may be erected as separate production lines. Some siderably; when circulation was resumed at high temperatures the economy in initial capital investment may be secured by color at once lightened. Oxygen enrichment of the air with reproducing the yellow oxide as an intermediate product and concirculation at 1:1 ratio gave an orange pigment; the throughput verting this t o the red oxide in an additional step. The washing was 0.5 gallon per minute. and drying facilities might be used in such a plant for both red The yellow iron oxides produced settle as readily as the red, and yellow oxide production. However, operating experience brown, and black oxides hitherto produced. They exhibit settling indicates that it is desirable t o design separate washing, drying, rates as high as 6 feet per hour and producc clear supernatant and bagging faciiities for the several colors produced. layers. Their particle size is very fine; they rub up satisfactorily Design estimates and quotations indicate that a complete with drying oils, exhibiting the same high oil absorption and tintoperating plant having these capacities for either color could be ing strengths shown in the reds, browns, and blacks previously built for a capital investment of $150,000, inclusive of light shelter described. but exclusive of site. The items included represent only actual Tests indicate that it is possible t o convert yellow oxide proprocessing equipment. Such a plant would very probably be duced by t h e methods described to red oxide in the continuous integrated with a larger plant such as a steel mill, steel processing red oxide pilot plant. Parallel plants might be constructed t o plant, or a paint or chemical specialties plant close t o a source of produce red, brown, black, and yellow oxide as independent pickle liquor. These large manufacturing or processing plants products, or one plant might be arranged t o produce red, brown, or black oxides with TABLE IV. CONTINT;OUS PRODUCTION OF YELLOW OXIDES yellow oxides as a possible inAir termediate product. Pressure, ECONOMICS OF THE PROCESSES
The economics of production of synthetic oxides by the processes outlined in this paper depend largely on rated plant capacity. A design study has been made of a larger plant rated at 8 tons per day of
Run 12
3c
Solution FeSO4 5 % FeSOd: 10% FeSO4 10% FeSOa:5% FeS04,5% batchwise FeSOa, 5%
5a 5b Ga
FeSO4,5% FeSO4 5% FeSOa:S%
la
2a 3a 3b
Temp., ' F. 135 160 120 68
Lb./Sq. Inch Gage 75 75 73 77 78
Throughput Rate, Gal./Min.
Recirculation Ratio
1.0
...
150
72
1.0
...
180 150 140
74 74 79
1.0
...
1.0 1.0 1.0 0.0
0.5 0.6
...
...
...
...
1.1 1:l
Color a n d Quality Dark yellow Dark yellow Dark yellow to light yellow Color Lixht darkens: yellow brown-yellow
Lightens rapidly from brown to yellow D a r k yello~v Progressivfly lighter t o light yellow Orange; air 2 5 % oxygen
678
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
would be presumed t o have ample supplies of electric power and steam available at relatively favorable costs. Steam a t 150 pounds per square inch gage saturated or a n equivalent heating medium is required. Electric energy is also required but in relatively small quantities; the heating energy costs outweigh those for electric energy several fold. Economic studies of the several alternative layouts and reactants considered for producing synthetic iron oxide indicate that the costs of chemicals is a relatively high proportion of the total cost of manufacture. The cost of heat is also a relatively high part of the manufacturing cost. Any factory by-product t h a t could be used as a chemical reactant or an especially low cost heat source would give this process a n additional profit advantage. Raw materials except pickle liquor were estimated a t prevailing commercial prices. Amortization allowances were included t o permit recovery of t h e original investment in as little as 18 months, Power and heat were assigned costs a t the highest commercial rates. On this basis, complete manufacturing costs indicate a comfortable margin of profit helow current market prices. This proportional margin should persist in the future. Markets. The products of this process are specification grade. They are salable not BO much by their mere availability as they are by reason of their consistent quality and uniformity. Research and production thus far accomplished indicate that continuous production by t h e methods outlined makes it possiblc t o produce a wide range of iron oxide colors with good Etandardization of color, hiding strength, and other desirable properties. The removal of the necessity for color matching of batches or of testing for other desired characteristics is believed t o be the strong advantage of pigments produced by this process. There seems no reason why production of pigments with specified physical properties cannot be undertaken by appropriate control adjustments of operating conditions. Economically, an ample margin of profit exists between the total cost of manufacture and the present market price of iron oxides. The present market contains a heavy weight factor in the form of 60 t o 75% of both domestic and foreign natural iron oxides. Two conflicting influences will affect the markets for the synthetic iron oxides. T h e first of these is the increased value of the inherently uniform properties possessed by oxides from continuous wet synthetic processes. The second is, of course, the law of supply and demand. The production of synthetic iron oxide pigments cannot possibly consume all the pickle liquor t h a t is available. One years’ supply of pickle liquor is sufficient t o several years’ requirements for synthetic iron oxide pigments a t current rates. It may be said, therefore, that synthetic iron oxides must be made a t a cost which will enable them t o be used in special applications not necessarily related to pigments. There are, a t present, several such applications for synthetic oxides. Magnetic recording tapes represent one currently well known and recent application of specification grade iron oxides. Magnetic particles as applied in electrofluid clutches may well come t o be another application requiring large quantities of synthetic magnetic iron oxide. More recently the use of synthetic iron oxide as a substitute for graphite in bearing lubricants has been reported. Other applications of aynthetic iron oxides await recognition of the peculiar properties of the various grades and colors of these materials. SURVEY O F THE LITERATURE
I n connection with continuing research in the field of synthetic iron oxide pigments! a review has been made of the literature to January 1, 1952. Several hundred papers containing significant references to the synthesis, physical or chemical properties, and utilization of synthetic iron oxide as pigments were assembled. This paper is divided into sections on (1) Physical Properties and Theoretical Aspects, (2) Precipitation Methods using Solutions of Soluble Iron Salts, (3) Hydrated Iron Oxides from Sulfur or Sulfide Reactions, (4)Synthetic Iron Oxide from Roasting or
Vol, 44, No. 3
Sintering Procedures, (5) Synthetic Oxides from Sludges Formed in Reduction of Aromatic Nitro Compounds, and (6) Iron Oxide Synthesis by Electrolytic Methods. The presentation is factual, no attempt being made t o assess the relative merits or demerits of any proposed process for producing synthetic iron oxide pigments. KO economic considerntions are discussed. SUMMARY
Tvo pilot plants, adaptable t o the production of various synthetic iron oxides from iron containing solutions such as wastc pickle liquors, have been described. The systems include mexiis for precipitating t h e iron s a h , for oxidizing them in a controlletl manner, and for converting the oxidized and/or precipitated materials t o the desired iron oxide product. Simult,aneous chemical reaction wit’h various precipit,ants and conversion from thc precipit’ated salt t o the hydrous or anhydrous oxide in aqueous suspension or solut,ion is accomplished by applica.tion of heat ;mil pressure in presence of chemical catalpste. The present pilot, plants have achieved capacities of approsi-mately 400 pounds per day. They operate continuously and reliably with little manual attention. Several varieties of oxidw have been produced. The continuous operation has been shown t o possese cost and operating advantages over bat,ch plants t,hus far reported in t,he literature. Design studies of an 8-ton eonimercial plant, based on the work thus far done indicate thc pro(:esses to be economically feasible when based on the various picklc liquor wast,es produced in iron or steel processing. ACKNOWLEDGMENT
Thanks are due W. B. Clippinger, whose aid and suggestione helped solve many mechanical problems in the constructinn and operation of these pilot plantg. BIBLIOGRAPHY
(1) Ayers, J. W., Can. Patent 379,225 (Jan. 31, 1939). (2) Ayeis, J. W., U. S.Patent 2,133,267 (Oct. 18, 1939). (3) Ball, F., Ibzd., 1,387,769 (July 26, 1921).
(4) DeWtt, C. C., and Livingood, A. D., “A Ciitical Survey of thc Recorded Literature on Synthetic Iion Oxide Pigments,’’ unpublished paper. ( 5 ) Elai, F. A., U. S. Patent 2,427,555 (Sept. 16, 1947). (6) Fireman, P., TND. ENG.CHEM.,17 603-4 (1924). (7) Fireman, P., U. S. Patent 1,424,635 (Aug. 1, 1922), (8) I b i d . , 1,490,372 (Aug. 15,1924). (9) Fricke, R., and Weitbrecht, G., Z . anorg. Chem., 251, 424 (1943) (10) I. G. Farbenindustrie, Belg. Patent 449,198. (11) I. G. Farbenindustrio, Brit. Patent 320,409 (July 12. 1929). 112) Lofland, E., U. S. Patent 1,924,127 (Aug. 29, 1933). (13) Marks, E. C. R., Brit. Patent 153,792 (Deo. 9, 1919). (14) Obladen, A., Ger. Patent 501,109 (Nov. 30, 1927). (15) Penniman, R. S.,Jr., and Joph, X‘. M., U. S. Patent 1,327,063 (Jan. 6,1920). (16) Plews, G., Ibid., 2,111,726 (March 22, 1938). (17) Ibid.,2,111,727. (18) Riskin, I. V., and Pugacheva, G , , J . Applned Chena. U.S.S.&., 11,1085-9 (1938). (19) Ryan, L. W., and Saunders, H. L., U. S. Patent 2,388,659 (Xov. 6,1945). (20) Schumpelt, E., Farbe, Lacke, u. Bnstrichstofe, 3, 46-50 (1949). (21) Storer, T., and Taylor, C. J. A,, Brit. Patent 290,421 (April 9, 1921). (22) Taffee, W. F., M.S. Thesis, Michigan Statc College (1949). (23) Uebler, B., Ger. Patent 658,020 (March 19, 1938). (24) Uebler, B., and Muller, R., Ibid., 658,843. (25) U. S. Dept. Commerce, Kashington, D. C., “Census of Rlgnufacturers,” T’ol. 11, Statistics by Industries p. 388, 1949. (26) Wurzschnitt, B., and Reuther. A , . Gcr. Patent 515, 563 (Dec. 5 , 1928). ACCEPTEDJanuary 18, 1&2. For material supplementary t o this article order Document 3568 from American Documentation Institute, 1719 N. Street, N.W., WaehipTton 6 , D. C., remitting S1.00 for inicrofilm (images I inch high on atandarq 35-1:11:1. :notion picture film) or $6.90 f o r photocopies (6 X 8 inches! readable witho u t optical aid.
RECEIVED September 17, 1951.
