Industrial Wastes
Brass alzd Copper Industry WILLIAM S. WISE State Water Commission, Hartford, Conn.
BARNETT F. DODGE AND HARDING BLISS Yale University, New Haven, Conn.
T . .
HE work of the State Water Commission IS concerned primanly with the zbatement of pollution of waterways by sewage and industrial wastes. The Connecticut law stipulates that any order requiring the abatement of pollution shall specify the particular system or means to be used and that the cost of installation, maintenance, and operation shallnot be unreasonable or inequitable. Because no practical processes for treating many industrial wastea within these specifications had been developed, it was necessary for the commission to undertake considerable research i n order to develop practical methods of treatment. The commission’s researcb and analytical work is carried out at two univmities in the state: metallurgical wastes, including those from the manufacture of iron and steel and of brags and copper, at Yale University, and textile, plating, tannery, and other miscellaneous wastes at Wesleyan University. Data obtained during the studes and researcb work on the treatment of wastes from the brass and copper industries are given in the following disoussion. This work covered a period of about eight yeam prior to the war and hae been resumed this year. Yankee ingenuity undoubtedly was an important factor responaible for loeating the center of the brass industry in the Naugatuck River Valley of Connecticut. The industry began in the Waterbury district during the end of the eisnteentb century where, prior to that time,pewter buttons and wooden clock movements were made. The substitution of brass for pewter in the manufacture of buttons. the obvious advantage8 of brags movement for clocks, the development df pinmking machines, together with abundant water power and wood for annealing purposes, r d t e d in the growth of the brass industry in this valley. The results of twenty years of persistat efforts and developments in the r o l l i of brass in Waterbury, around 1800, definitely establied the center of the brass industry there. In 1880 over 75% of the brass and copper products manufsdured in the United States were produced in Connecticut. The establishment of industries in other sections of the country had reduced this w e to 66% by 1925. Although more brass end copper products me being made in Connecticut today than ever before, they represent only about B third of the total produced in the country. Thkdisdonwillbelimitedto themanufactureof those metSLS and alloys produced by the copper and braaa industries, such as plates, sheets, and strips produced by ro@g opsrations, rode and wire produced by extrusion and drawing operations, and tubes produced by piercing or extrusiou-and drawing. The p h oipd alloys used in the fabrication of these products include ordinary braes (oonsistiinp of about two thirds copper and one third sine with small amounts of tin and I d ) , special brags with various amaunts ofalloying metals, lead braes, bronze, silicon bronze, phhepbor bronze,cupronickel, nickel silver, aluminum brsaa, and other alloys which indude chromium, tellurium, beryllium, manganese, etc.
The operations med in the manufacture of these products (4) are uniform throughout the industry, witb minor modifications within individual plants to suit special conditions and requirements. The raw materia+ are obtained from refineries in the form of ingots, billets, bars, and slabs. The charges to the furnace are compounded from these raw materials and scrap of various alloys either produced within the plant or purchased from other fabricators. Many years ago these charges were melted in graphite crucibles holding up to several hundred pounds and were heated over pit fires. About t h a y years ago the electric furnace came into use with heat produced by low frequency electric current. Modern furnaces have capacities of molten metal up to 2000 pounds or more. In effect the electric furnace consists of a transformer of which the secondary circuit is a refractory channel filled with molten metal. The main body of the furnace forms the primary circuit. Before the furnace can be started, it must be partly filled with molten metal from another furnace. Current flowing through the primary circuit induces a current in the secondary of su5icient intensity to raise the temperature of the metal comprising it. At the same time a vigorous circulation, due ta electrical forces, is set up in the vessel containing the molten metal; this ejects the superheated metal into the main body of the furnace, thereby melting cold metal as it is charged into the furnace. The molten metal is then noured into molds of various sizes and sham to produce billets or bar castings for further operations. The bar rastines - arc rolled intu dates. slcets, and atritx USUW in three operations: breakdown roll, rundown roll, and finishroll. In modem mills the rolling operations are largely coutroUed by push buttons and witb mechanical handling devices. After breakdown rolling, the dabs or bars are overhauled in heavy slab d e r s or overhauling machines, where the surface is removed to the thichess of surface defects. The chips thus removed become scrap for use in making up charges in the electric furnaces. The rundown rolling is usually done on tandem four-high mills. Finishing is done on four-high and two-high mills according to requirements. After a certain amount of rolling, the metal becomes “bard” and must be annealed before further rollihg. Pickling is required to remove the oxide scale or stain which re= sults from a n n d i . Rods and wire are formed in an extrusion machine. This machine consists of a horizontally arrangedhydraulic press o w a t i i under pressurw up to 60W pounds per square inch. One portion of the machine is a heavy-walled cylinder closed a t one end by a die. A heated billet is placed within the cylinder; then the plunger forces the metal of the billet through the die in the form of a rod. The extruded rod, after pickling, is given a finishing draft on a block or drawbench. Reduction to smaller sizes for rods and wire requires drawing, through dies, on a wire blcck. Here again the metal becomes bard after certain reduc-
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tions in size, and must be annealed and pickled before further drawing. Tubes are formed by basting a hollow shell using a sand core, by piercing solid cast bars or billets, or by extrusion. The latter procesa is in general use today, particularly 03-alloye which cannot easily be pierced, and this is done on a modified rod extrusion machine. The modification includes the addition of a second p m u r e cylinder oariying s'piercmg mandrel with a diameter equal to the required inside diameter of the tube. After the billet is placed in the main cylinder, the piercing mandrel is advanced until the billet is completely pierced, then the mandrel and extrusion plunger travel together until the tube is extruded. Annealing and pickling are necessary during the drawing operations on tubes similar to those described for wire. Annealing operations were originally carried out in woodfired furnaces; later oil and gas were used to furnish heat. During the heating and cooling of the metal a rather heavy scale formed on the surface because of oxidation of the metal. The modern annealing furnaces are oil-6red.andbuilt 80 that the metal is heated and cooled in a controlled atmosphere or in a reducing atmosphere by using reducing gases. This substantid1y reduces the m o u n t of oxide scale. These furnaces are coming into general use not only because they practically prevent the formation of scale under certain conditions but hacause, through better temperature control, they produce al10ys with different properties t o meet specifications. Scale formed on the surface of the metal is very hard, and therefore must be repoved before the rods, wire, and tubes are dram to prevent damage to dies, and before sheets and plates are rolled 80 the scale will not be embedded in the finished material. This is removed by pickling in a bath made up usually of 5 t o 10% of sulfuric acid by volume. Stain, are also formed and must he removed, particularly on the finished product. This is done in a "bright dip" solution composed of 5 to 10% S d f U r i C acid and 0.25 to 0.5 pound of sodium dichromate per gallon of solution. After the metal bas remained in the pickle and bright dip sohtion8 for the required lengtb of time it is removed and rinsed in tanka through which clean water is flowing in substantial volumes. These rinse waters continuously discharge to drains which, in .turn, u s d y empty into rivers. During pickling and bright dipping, the scale and a certain amount of the base metal are dissolved. This CSUS~S decrease in the concentration of free S d f u I i C acid and an increase in the canoentration of dissolved metal. The solutionsare strengthened from time to time with additional acid and dichromate, but when the concentration of dissolved metd and, therefore, the length of pickling time increase to a cer$ain point, the solution8 are dumped to drains as spent solutions, and fresh mlutions axe made up. The frequency of dumping depends largely upon the composition of the metal, the length of pickling time, and the amount of metal pickled. +ne bright dip solutions must he dumped daily, others less frequently, wberess the pickle solutions may be used.for a month, more or less.
.lu5t.y which lead to W a S t e S of various kind5 are iewed briefly and figures given on t h e amounts ulfurio acid, sodium chromate, and metallic z mnd copper consumed or lost in one year. Data h e limiting concentrations of t h e main coin tents in both the concentrated and the dilute wi iquors from t h e pickling of brass are prese t is shown that, for one plant a t least, a p p nately WYo of t h e pollution load was in t h e d i vastes 01 rinse waters. One of t h e treatment pi .sees developed in t h e Chemical Engineering Deps nent of Yale University and tested i n a pilot pla I t one of t h e brass mills is outlined, and a fea cos 'mates are given. Further s t u d y led to t w o otllp, are illustrated b) flow < s in one of these procei
. metal in the furnace. These skimming8 contain the metals composing the charge and may account for 1% to as much as 5% of the charge. Approximately 50% of these metals are rewvered in the reclaiming plant and mused; the remainder is shipped t o smelters where the copper ia recovered and returned to the industry. The zinc is not recovered and therefore is a loas. Rolling and dkawing operations produce scrap in the form of &erha&g ohips, which are re-used. ,The amount may be &s much 88 S%, pmticulmly from the rolled plates or shbs. Any male removed from the m d e d metal in quenching o p erations is easily rewvered and readily salable. The remaining lasses in pickling operations consist of dissolved metals, the amounts of which are @veri in the following tables. The total shrinkage in the mill (difference between the weight of hished metal shipped and the weight of metal purchased) is about 2.5%; some of this is shrinkage due tb oil and inert m k teria1,in the scrap purchased, inacmwiea in weighing, etc. In 1941 the State Water Commission made a survey of the various losses from the brass m d copper industries in Connecticut. It was estimated that these industries produced between 575,000 and 600,WO tons of finished m+terial in that year. The data obtained during this survey are shown in the following table: 10,250
i~ao
11 600
3-20
ZD-60 20-40 4,200
3,lW a.126
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WASTES AND BY-PRODUCTS
The water-borne industrial wastes from operations of this nature obviously are large in volume. A p l a t producing in the neighborhood of 50 ton6 per day of hished metal may require from 3000 to 6000 gallons per hour for pickling and bright dipping operations. Substantial volumes are used in other operations, and result in oil baaring wastes and vari?us substances from the aorsp reclaiming plants. Melting operations produce two by-products. Zinc oxide is produced by volatilizatiou of a portion of the siuc in the electric furnaces. This material is targely wasted through the furnam into the atmosphere as a white smoke; the logs represents about 0.5% of the zinc charged to the furnace. The other bythe top of the molten product is in the form of skimmings
1,lW LIQUW WASTES F a o M PICKLING OPERATIONS
During 1940 a survey was made at one of the large W r y p h t s in Connecticut to determine the nature of the wastes produced in pickling operations. The variations in composition of these wastes are indicated in the following tables. Samples collected from each of eight pickle tub8 (capacities, 1100 gallons) prior to dumping showed variations as follows in grams per liter:
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Similar samples from each of nine bright-dip tanks (capacities, 300 to 1100 gallons) prior to dumping showed in grams per liter: Sulfuric acid Copper Zinc
5 . 6 to 85.8 6.9 t o 44.0 0 . 2 to 3 7 . 0
Chromium, hexavalent Chromium, total Iron
4 . 3 to 1 9 . 1 13.5 to 47.7 0.03 to 0.36
The analyses of samples collected from rinse water drains for a 24-hour period shorn-ed hourly variations as follows in paPts per million:
Iron
Tube 11111 4-209 34-147 19-73 0-5 3-78 1-5
Rod and
TT ire LIi11
192-4942 385-1582 350-4300 0-67 345-1100 9-93
Rolline RIill 140-1997 10-87 28-112 0-35 6-84 1-13
Calculations made from thebe analyse> and the volumes shon-ed arid and total metal loss from pickling operations as follows:
This survey not only produced information with an important bearing on the waste treatment process but revealed the surprising fact that the major portion of the pollution load, and by far the greatest acid and metal loss, occurs in the dilute wastes. Industry itself held quite the opposite viewpoint regarding the proportionate losses in the strong and dilute wastes. The survey, therefore, resulted in placing more emphasis on the importance of the dilute wastes in the solution of the treatment problem. EFFECT O F WASTES
The effect of these wastes on waterways is fourfold: (a) Their effect on waters used for public water supplies for industrial, agricultural, and recreational purposes is obvious. ( b ) The acids and met'als in solution are toxic t o aquatic life, even in small concentrations, in the soft waters of New England. Higher concentrations can be discharged into hard waters without exceeding lethal limits. It is usually considered for soft waters that a continuous acid concentration stronger than p H 6.0 in a receiving stream is lethal to the lower forms of aquatic life which furnish food for fish, and therefore is also lethal to fish. Concentrations of copper, chromium, zinc, etc., greater than about 2 p.p.m. are usually considered lethal t o aquatic life. (c) These wastes also affect the natural sequence of processes necessary t o bring about self-purification of streams. Inasmuch as practically all streams receive some pollution, natural or artificial, it is important to prevent conditions that would inhibit natural purification. ' ( d ) Suspended solids, either in the wastes or formed by chemical reactions in the receiving water, blanket' the stream bed and destroy aquatic life. -4stream which cannot support aquatic life is an unhealthy stream. When these wastes are discharged into sewerage systems above certain concentrations, they seriously affect the systems by causing deterioration and eventual collapse of the sewers. Furthermore, they cause corrosion and deterioration of the sewage treatment plant, particularly the mechanical equipment, and seriously affect biological treatment of sewage, generally the most economical method of treatment in use t,oday. TREATMENT OF LIQUID WASTES
The State Water Commission has always attacked the industrial n aste treatment problem with two ends in view: abatement of pollution to a degree that will satisfy the requirements of the stream, and recovery of by-products of value. Research directed toward this goal was started a number of years ago on the treatment of wastes from the brass and copper industries in this state. However, it had to be abandoned during the war. This research has gone through several phases, and during each phase many angles have been studied. One of the important
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studies was made in 1934 and 1935 when a pilot plant w a a operated a t one of the large industries in the state t,o develop a method of treatment, based on previous laboratory studie-. The plant treated strong Tvastes combined with dilute nxstea. It had a capacity for treating 10 gdlons per minute: the result, were summarized in biennial reports published by the conimission (1). The vast'es were pumped from the main mill drain, which carried the x-astes and rinsr waters together with large amounts of other diluting waters. Briefly the trratmrnt conqisted of the f~liii\riiigctrIh: 1. Equalization to minimize large fluctuations in concent ra tion. 2. Reduction of hexavalent to trivalent chromium 1 , ~ . sulirir dioxide in order to make it possible to precipitate the total chromium. 3. Deposition of the copper on brass chips whereby the ziiic in the chips is replaced by copper. Under favorable conditions this removed practically all of the copper which was present, in the wastes. 4. Keutralization of the copper-free wastes with lime, and precipitation of chromium, zinc, and the other alloying metals present in minor quantities. 5. Dewatering the sludge on pressure filters. 6. Addition of soda ash.to the dewatered sludge and roasting the mixture in a gas-fired furnace to oxidize the chromium t o the hexavalent form. 7. Leaching out the chromate with water in a form usable in bright dip operations. 8. Extraction of the zinc as electrolytic zinc or as zinc sulfate for resale.
Steps 5, 7, and 8 were carried out in the Chemical Engineering Laboratory of Yale University. The cost of building sucli a treatment plant to handle a flow of 3,000,000 gallons per 24 hours Tvas estimated at $200,000, with annual fixed charges and operating costs of $79,300. The value of the recovered products was estimated a t $55,800, leaving a net annual cost of $23,500. The5e figures were based on 1934 prices. hfter'operation of this pilot plant, research studies were directed toward two different lines of approach: regeneration of strong chromate waste pickle liquor for direct return and re-use, and concentration of t,he metals in the more dilute rinse waters to the point where they could be mixed with the spent pickling liquors for further treatment and recovery. During the bright dipping operations the hexavalent chromium is gradually reduced to the trivalent form. Electrolytic regeneration is essentially a reversal of these chemical reactions. Figure 1 is a flow sheet indicating the various steps necessary in the regeneration process ( 3 ) . Many difficulties are inherent in the process; nevertheless e x periments indicate that regeneration offers a possible solution to the recovery of the spent wastes. One of the difficult problems that remains to be solved is that of the cell diaphragm, which should have a high resistance t o diffusion but low electrical resistance, must resist attack by the highly oxidizing conditions in the liquor, and should be relatively cheap. Ceramic materials, fabrics of glass and of synthetic plastics, and two parallel fnbri.cs separated by a small space filled with filter aid to form a stagnant layer of the electrolyte it,self have been tried with varying degree5 of success. Further studies will have t o be made to determine whether the necessary residual zinc concentranon in the regenerated liquor, if re-used, xould interfere with the pickling process. It was found that satisfactory deposits of zinc could be obtained on the cell cathode. It will be necessary to carry on further work on a pilot plant scale to obtain more definite and conclusive information regarding the practicability of the process and its cost. After operation of the pilot plant, further laboratory st,udies led to the development of the two alternate processes shown in the flow diagram of Figure 2 (3). A pilot plant is now being set up a t another of the large plants in the state which incorporates the steps in the first part of the process show1 in Figure 2, including the production of dewatered sludge on a vacuum filter. The sludge thus produced will be used to continue the experi-
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Figure 2.
Flow Diagram for Treatment of Brass and Copper Mill Wastes
merits in ehecldng and obtaining more definite information on the various steps of the complete treatment process. Although not indicated i n Figure 2, equipment is now being installed in the pilot plant for studying the application of the ion exchange principle t o the concentration of metals in the dilute wastes. Synthetic resins will be used as the ion exchange medium, and it is expected t h a t further useful information will be obtained concerning the utilization of these rnateriah in the treatment of industrial wastes. The company is contributing generously in setting up and operating the pilot plant. The data that wiI1 he aceumulsted will undoubtedly supplement the information previously oh-
tained. This type of cooperation of an industry with a state agency e m he expected to produce a feasible solution of the problem. LITERATURE CITED
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(1) State Water Commission, Hartford, Conn., 6th Biennial Rept.,
1934-6. (2) Ibid., 8th Biennial Rept., 1938-40: 9th Biennial Rept.. IS40-2. (3) Stepnek, J. E., “Reoovery of Metals from Brass Mill PicLliq Wash Water”, Report, 1942. (4) Webster, W. R.,Metals Tech., June 1942. PBEBENTED before the Industrial Waste Symposium at the 111th Meetins of the Aumnrcm C a e ~ l c SOOIETT. u Atlsntio City. N. J.
