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NDUSTRY w ill always have the problem of dis sing of its waste materials. As new processes are develo r n e w wastes are created and older processes, together with t&r wasteesubstances, are often made obsolete. Consequently the resldual substances coming out of our industrial fabnc are changing constantl in amount type, and kind. Uti$zation of t6e wastes of industry can be attained either within or without the industry producing the residual substance. The most desirable method is to use the wftste in the. plant rpducing it. Tremendous m o u n t s of materials are bemg use2 in plants where, not many years ago, they were considered uneconomic materials. There are instances within every industry where a wagte has been used advantageously. The substance, which was once a residue, now becomes the by-product. Each byproduct was once a humble industrial waste which aased through the stages of technological investigation in orfer t o become elevated t o the status of a by- roduct. Cases can be cited where such by-products have often fecome the main product in an industr as a result of technological prqgress and change. Ruiber manufacture is an mterestmg example of 89 industry which consumes its own waste. About thirty years ago when automobiles became rather lentiful, the accumulation of worn tires became a problem. gubber tlres are composed Qf three major parts, the tread which is solid rubber, the carcass or fabric portion containing highquality rubber in which the tire fabric is embedded, and the run or “bead” which consists of steel wirfts set in a core of hard rubber wra ped with a rubber-coated fabpc aa the outer cover. At first o~$y the tread portion waa considered usable. Operators placed the tire over a wooden circular frame and skived the tread from the carcase with shftrp h v e s whetted with water. After the tread waa ground mto small crumbs, it was mixed with mineral and vegetable oils, and then heated in open steam autoclaves to soften the rubber. After drying, this product wm milled to abuniform l y t i c mam for incorporation mto standard rubber t u e form&tions. It was necessary a t that time to dispose of the carcaa and be$ portion of the tire as a waste material. When l v g e piles of t+ residue were burned, they made spectacular r a g 9 bonfires whch challenged the ingenuity of the few chemists mthin the organization. Research soon found the answer. The rima were cut from the c a r c w , and the carcass wm ground to small pieces and heated in a strong caustic solution under pressure, with oils added to soften
the rubber. After washine; and drying, the product from this di estion was milled t o a uniform mass which w v good reclaimed ru%ber. Later it was found best to cut the rim from the old tires and rocesa the tread and carcms portions. together in this caustic sorution. A substantial amount of recltumed rubber has been produced by this method. Then only the runs of the tires remained m a problem for disposal, because the steel wve reinforcement was difficult to remove and the hard rubber core was not readily softened by known chemi’cals. The rims were carried to dumps along with other plant refuse and buried in the dirt and ashes. Huge dump areas were created. Here &gain chemistry came t o th? front with its ally engineering. Eqw ment was devised for stripping the steel wire from the rims, new s o f e x y chemica!s were. found for the hard rubber portion. The diamte rated p ~ , . m t h o u tthe steel wire, were heated with alkak andgsoftemng. oils for a long period in steam, under pressure to make a reclaun rubber suitable for use in man mechanical products. .Thus the entire portion of old automotile tires WM utih.zed w i t h the rubber industry. But the reclamation of old tires is now about to change agam. Synthetic rubber cannot be processed by the same methods aa natural rubber. New reclaiming methods must be found in the laboratory which are capable of softening and devulcanized synthetic rubbers. This will not be easy t % t B s t r y will find t h e answer. Some may think that chemistry can help only those industries eng ed in chemical manufacture or those related t o chemistry. L e t x e m coneider the aase*of a mining industry which did not we chemicals in any operptions. In the production of phosphate rock in Florida, the rock is crushed the m d is washed out, and the crushed product ia webscreened t o obtam ground phosphate rock for shipment to fertilizer lants. The water used in washing contains, in addition tq s a d a considerable portion of finely divided phosphate perticles which are too small for collection on the screens. (Continued on page 98)
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Harold R. Murdock is a consulting chemical engineer who has been engaged in industrial research and manufacture for over thirty years. During the past sixteen years he has been director of research for one of the countryk largest pulp and paper mills. H e was also vice president and general manager Qf a company manufacturins organic mercurial compounds for use in both the medicinal and industrial fields. His experience has been diveniAed. His knowledge of the chemical treatment of wood, the reclamation of rubber, the manufacture of intermediates, dyestuffs, and pharmaceutical chemicals, the compounding of varnishes and lacquers, and other activities, has served as a reservoir of experience to aid him in the interpretation of problems In industrial waste, a subject in which he i s now a specialist. His headquarters are at Asheville, N. C. The editors welcome him to the staff of contributing editors, and know that his monthly column on indurtrial wastes will be valuable to others in this field.
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The spent water, containing sand and fine phosphate, is discharged to large lagoons to settle out the suspended matter SO that the clarified water can be re-used. These lagoons fill up with sediment, and new lagoons are made from the pits resulting from the mining operation. Until recently this finely divided phosphate rock in the lagoons has been lost. Chemists have recovered this value by flotation of the sediment dug from the lagoons with mineral oil containing oleic wid. Cheaper substitutes which contain fatty acids related to oleic acid, such as the tallol recovered from the pulping of southern pine, have made this process economical. Now these dum s of sand and finely divided phosphate rock are being reclaimed t y flotation tables and fatt -acid-containing chemicals. Txe utilization of waste materials in industries other than the one which produces them has tremendous possibilities. Such opportunities are often overlooked by industry. This type of application requires a high degree of in enuity and resourcefulness, an insatiable curiosity, and a broadgunderstanding of the processes existing in other manufacturing establishments. The chemist can be of particular help in this method of finding an economical use for a waste material. Some years ago the writer was associated with a wood pulp mill which was erecting a plant in a new location, The plant was to operate the so-called kraft process commonly used in pulping pines. The chemical generally utilized in the kraft process is sodium sulfate in the form of salt cake. Rather than p u r c h w the customary chemical, it was suggested that the organization look about for substitute waste materials. Many of the d salt lakes reasonably close to the mill site were investigat3 In a11 of these de osits sodium chloride was found aa a contamination of the GlauBer sait. A method for separating these salts was necessary, and Glauber salt had to be dehydrated to sodium sulfate in order that a suitable substitute for salt cake might be obtained. This operation re uired a rather substantial investment and it was recommendel that the search be continued. It happened that this mill was also installing a phlorine plant to bleach the pulp to high whiteness. The chlonne was to be made by the electrolysis of sodium chloride in the conventional way, which yields by-product caustic soda. By the orthodox method of eva orating the cell liquor .and separating sodium chloride cryst& from the caustic solution w eva oration proceeded, a commercial rade of caustic soda could%e produced. We learned that oil re&eries used caustic soda solutions to remove hydrogen sulfide as well as other organic sulfides from the crude oil, and that the residual caustic solution was relatively concentrated. This waste product from the oil refineries was a dark tarry solution composed essentially of sbdium sulfide and other sulfur-containing sodium salts. It was foul in odor. When added to the stream it created a serious roblem for shipping and was a nuisance t o riparian-right owners $ownstream for many miles. The B.O.D. value of the waste was high, and an oily tarry matter separated from the aqueous portion of the waste upon dilution with the brackish waters of the stream. The refineries were in a des erate situation. State authorities had brought suit for the &atement of the nuisance. Skimmifig tanks and other such procedures had only partly solved this aggravating problem. Refinery officials were only too glad to listen to the pulp mill chemist who offered to buy this stinking black tarry residue. The processing of a kraft mill to regain the chemicals for subsequent use is essential $0 the economy of the process. Briefly, this recovery of chemicals consists in eyaporathg the spent hquors from the pulp washing ste then inclnerating the concentrated solution and simultaneousg adding salt cake to these liwors. The organic matter present in the black liquors reduces the sodium sulfate to sodium sulfide dying incineration. The process is completed in a smelter type furnace, and molten sodium carbonate and sodium sulfide flow from the smelter into dissolvin tanks. It was apparent that the oil refinery w y t e solution coud be used in a process of this type. The refineries were asked to concentrate their waste solutions moderately t o make it economical for shipment to the pulp mill. The new make-up chemical worked admirably in the pulp mill operation. Some of the advantages of the refinery product were not full a reciated ?til the material wm actually used in the kraft mill &S apphcatlon was possible because of an understandlng of the pulp mill processes. If the oil refineries had posseawd such information, they could have overcome their waste disposal problem sooner and avoided litigation and other contributory nuisances: Certainly other industries and other waste materids have similar chances for utilivation if their problems are studied carefully. 98
