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University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Masters Theses Graduate School 8-1938 An Investigation on the Sulfuric Acid Leaching of Low Grade Rock Phosphate David Weldon Reed University of Tennessee - Knoxville Follow this and additional works at: https://trace.tennessee.edu/utk_gradthes Part of the Chemical Engineering Commons Recommended Citation Reed, David Weldon, "An Investigation on the Sulfuric Acid Leaching of Low Grade Rock Phosphate. " Master's Thesis, University of Tennessee, 1938. https://trace.tennessee.edu/utk_gradthes/3050 This Thesis is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by David Weldon Reed entitled "An Investigation on the Sulfuric Acid Leaching of Low Grade Rock Phosphate." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Master of Science, with a major in Chemical Engineering. Robert M. Boarts, Major Professor We have read this thesis and recommend its acceptance: ARRAY(0x7f6ffe7828a8) Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) August 12, 1938 To the Committee on Graduate Study: I submit herewith a thesis written by Mr. David Weldon Reed and entitled Investigation on The Sulfuric Acid "An " Leaching of Low Grade Rock Phosphate , and recommend that it be accepted for eighteen quarter hours credit in partial fulfillment of the requirements for the degree of Master of Science, with a major in Chemical Engineering. Major Professor At the request of the Committee on Graduate Study, we have read this thesis, and recommend its accep�ance. Accepted for the Graduate Committee .?----./ Dean AN INVESTIGATION THE ON ACID LEACHING SULFURIC OF LOW GRADE PHOSPHATE ROCK -·o - Q " 0 - . , -. A THESIS .. , . �� • : 0 . -. • • •• oc Submitted to the Graduate Committee of T.he Un ivers ity of Tennessee in Partial Fulfillment of the Requiremen ts for The Degree of Master of Science by David Weldon Reed A.ugus t 1938 A.CKNOWLEDGMEN T The author wishes to acknowledge the helpful gnggestions and unprejudiced cri­ ticisms so generously given by Dr. Robert M. Boarts in the course of this investigation. :155599 1 CONTENTS page INTRODUCTION 1 �URPOSE AND PLAN OF ATTACK 5 LITERATURE 9 EXPERIMENTAL RESULTS 14 Phosphate Rock From Hickman Tract 14 Introduction 14 Experimental Procedure and Apparatus 16 Effect of Concentration of Acid, Fer Cent Excess, and Time of Recovery ofP205 21 Effect ot Temperature on·Recovery of P205 24 Effect of Particle Size on Recovery of P205 26 Recovery of Acid 28 Discussion 29 Phosphate Rock From Johnson County 31 . Introduction 31 E:xperimental Procedure and Apparatus 33 Effect of Cone en tra tion of Ac i&>., Per Cent Excess, and Time, on Recovery of P 0 33 2 5 Discussion 35 11 CONTENTS ( continued ) Phosphate Rock From Perry County 36 Introduction 36 Experimental Procedure and Apparatus 38 Discussion 42 CONCLUSIONS �3 BIBLIOGRAPHY · 45 APPENDIX 46 INTRODUC TION The practice or using phosphatic materials as fertilizers goes back so tar there is no record of when and where they were first employed. The dung of 1 birds was used over 200 years B.C. The use of bones is also an ancient practice. T.hese materials continued to be the main sources of phosphorus and phosphoric acid until after the middle of the nineteenth century, when the Napole�nic battlefields, which had been a source of bone, could no longer be worked profitablf'·:i The treatment of phosphatic materials with sulfuric acid was first suggested by Liebig in 1840. In 1842 Lawes took out the first English patent for acidulation ot bones and later the same process was applied to rock phosphate. Mineral phosphates known as coprolites were dis­ covered 1n England in 1845 and in France seven years later. Rock phosphate was first developed 1n Iouth Carolina in 1867. Since that time the United States has been the foremost phosphate producing nation in the world. The chief deposits of rock phospbate 1n this 1. Waggaman, W .H. and Easterwood, H.W . , Phosphoric Acid, ---- Yhosphates, and Phosphatic Fertilizers, p. 16-18 2 country are loca ted in Florida, Tennessee, Montana, Utah, Wyoming, and Idaho. Other important deposits have been found in Belgium, Germany, Spain, Russia, 2 Algeria, Tunis, Egypt, and Morocco • The most extensively exploited deposits of phospha te in the world are those of Florida. The ph ospha te deposits of thi s country which rank next to Florida in commerc ial importanc e are those of Tennessee. Tennessee is well situa ted for the distribution of fertilizer material to the southern and middle western sta tes. Its phosphate depostts occur in the central basin of Tennessee and in the western part of the Highland Rim. The area covers appr oxima tely 7000 square miles. Most of the phosphate rock marketed in 1936 came fr om the brown-roc k fields ot Maury, Sumner, Giles, Davidson, and Hickman counties3. C onsiderable blue rock was shipped fr,om Lewis and Sick- ,. man counties, and a little whi te rock fr om Perry County. There are three economically important types of rock ph ospha te in Tennessee, namely, the brown, blue, and white pho spha te. The.deposits of br own rock ph osphate are genera lly conceded to be formed from ph ospha tic limestone by the wa shing out of the more soluble car­ bona te of lime. The blue rock is a conglomerate deposit 2. Bear, F.E., Fertilizers, p. 190 3. Hughes, H.H., Minerals Yearbook (1937), p.l319 3 derived in part from the underlying Ordovician limestone n and partly tram remai s of later marine life. T.h� white phosphate has been divided into three 4 classes by Hayles , namely, the stony, breccia, and lam--· ellar varieties. The latter is the richest and most plentiful. T.he breccia variety consists of chert frag­ ments imbedded in a ma. trix of high grade phosphate. The stony phosphate co nsists of silicious skeletons formerly filled with c·arbonate of lime but now containing phos- phate. The two commercially important acids used in acidula­ tion of rock phosphate today are sulfuric and phosphoric acids. Phosphoric acid is derived from the rock itself. The 1Wo distinct methods of producing phosphoric acid are, first, the sulfuric ac id process and, second, the volatil­ ization process. ln the sulfuric acid process phosphoric acid is produced from the tricalcium phosphate of the rock .as shown in the following reaction: The te�, leaching, as used throughout this paper will refer to the process in which the above reaction takes place. 4. Waggaman, W. H. , and Easterwood, Henry W., loc. cit., p. 74 4 In the vola tiliza tion process sil ica and coke are ° added to the rock· and the mixture hea ted to about 1500 0 either by burning part of the coke in a blast furnace or· by heating with an electric arc. The general course of this reaction is usually represented as follows: To produce ph osphoric acid from the phosphorus vola til�zed 1n the above reaction the phosphorus is oxidized to. ph osphorus pentoxide and_this oxide hydrolyz­ ed to phosphor ic acid . Much of the phospbate'rock in Tennessee is of such low grade that if it were simply acidu1a ted with sulfuric acid the resulting superPhosphate would be too low in plant food value to warrant extensive distribution • . T.he vola tilization me thod ha s not yet been developed so that it can use the low grade rock satisfactorily . The sulfuric ac�d process is probably best adapted tor the utiliz� of low grade rock phosphate . For this rea s on, an inve sti�tion on the leaching properties of three low grade rock phospha tes wa s made. The low grade rock phosphates chosen were tram Hickman, John s on, and Ferry Countie s of Tennessee . 5 PURFOSE AND PLAN OF ATTACK The manufac ture of ac id phosphate is one st�p in the pr ojec ted method for the utilizat ion of a low gra de rock ph ospha te . For this reason the chemis try of acid phosphate manufac ture will be discus sed briefly here. Sup erphosphate is the produc t' forme d when rock ph os­ phate is ac idulate� with sulfuric acid. T.he term triple superphosphate is used to denote the produc t formed when rock phospbate is acidulated· with phosphoric ao id. The term acid ph ospha te, general ly thought of as super­ phosphate, will be us ed throughout this the sis to denote the pr oduc t made by ac idula ting rock with mixtures of sul­ _furic and phosphoric ac id s. The ph osphorus in rock phospha te is ac tually in the form of fluorapa tite, ca5(P04)3F, but for calculati on purposes it is assume.d to be combined as tric alc ium ph osphate, Ca (F0 ) • 3 4 2 When the tr icalc ium phosphate is reac ted on by sul­ furic acid the following reac tion tak es place: 6 When tricalcium phosphate is reacted on by phosphoric acid the following reaction takes place: In the ma.nufacture of ordinary superphosphate an insufficient amount of sulfuric acid is added to the phosphate rock to change all of the tricalcium phosphate to calcium sulfate and phosphoric acid.

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