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INDUSTRIAL AND ENGINEERING CHEMISTRY
principally on economio considerations; these have been dealt with in a previous paper ( 8 ) . Magnesia can be used to treat pickle liquor where recovery of iron oxide and magnesium sulfate is economically sound. The small volume of sludge and the fact that it can be washed by continuous decantation are of great advantage for this compound. The by-product and the simplicity of the operation may offset entirely its rather high cost. High calciumlime a t last can be used in a manner that d l separate quickly a considerable volume of supernatant liquor for discharge from a sedimentation basis. Also, where it is necessary to dispose of the sludge by trucking it to a dump, this agent yields a slurry that filters rapidly to a cake of low moisture content. Dolomitic lime falls midway between magnesia and high ea!cium lime in final sludge volume. The choice between this agent and high calcium lime will depend wholly on local conditionsfor example, in some areas dolomitic will be in much better supply than high calcium lime. Oxidation rate and agent reactivity are the principal controlling factors in the process. With high calcium lime where the halfstrength pickle liquor rate Tas increased from 283 to 310 ml. per minute the supernatant liquor contained no soluble iron, but the ferric to ferrous ratio fell below 2; here the oxidation rate controlled the pickle liquor rate. With dolomitic lime, the pickle liquor rate had to be reduced to 108 ml. per minute to get 8 substantially iron-free supernatant liquor; here the reactivity of the alkaline agent controlled the pickle liquor rate. With a reactive magnesia the controlling factor usually will be a function of the excess of that agent used. The number of possible variables in the process is too great to r t l l o ~completion of a systematic study of all of them. Such a study would not be warrantcd in any case because of the varia-
Vol. 41, No. 1
tions in local conditions. The salient features of t8he process have been pointed out in this paper, and adaptation of the process to a particular mill should occasion no difficulty. For optimum results, the supernatant liquor should contain little or no soluble iron; the ferric to ferrous ratio should be in the range 2 to 6, preferably 2.5 to 33; and the reaction temperature should be above 75” C., preferably above 80’ C. The operation of the process on a continuous basis can be accomplished readily by installing equipment for feeding the alkaline agent a t a constant rate. Such operation would be attractive at many mills and the problems involved mould be of an engineering rather than of a chemical nature. T r i a k w i t h reactors of various sizes have disclosed, in the reactor sizes studied (4, 6, 8, and 12 inches in diameter), the volume of pickle that can be handled is proportional to the volumetric capacity of the reactor. If this relat,ion holds for large sizes, a simple calculation shows that a reactor 7 feet in diameter by 20 feet high would handle 10,000 gallons of strong pickle liquor per &hour day. This illustration is given merely to provide a basis for visualking the probable size of a neutralization plant. ACKNOWLEDGMENT
This work was undertaken as a part of the research program of the Stream Pollution Committee of the American Iron and Steel Institute through the Multiple Industrial Fellowship sustained at Mellon Institute since 1938. LITERATURE CITED
(I) Koa&, R.D., Lewis, C. J., Sindlinger, C. J., and Klein, B., IND. ENG.CHESII., 39,131 (1947). (2) Ibid.,40, 2062 (1948). (3) Wilson, H. R. ( t o Natural Carbon Co.), U. 9. Patent 2,419,240 (hpril 22, 1947). RECEIVED December 8, 1947
E. T. JIGBEE, MUBEKT M.HILL’,
AND G. BRYANT
R4CHMAN
Purdue ITniuersity, La
