(k Bureau of Mines Report of investigations/l984 A Basic Chloride Method for Extracting Aluminum From Clay By P. R. Bremner, L. J. Nicks, and D. J, Bauer UNITED STATES DEPARTMENT OF THE INTERIOR Report of Investigations 8866 A Basic Chloride Method for Extracting Aluminum From Clay By P. R. Bremner, L. J. Nicks, and D. J. Bauer UNITED STATES DEPARTMERIT OF THE INTERIOR William P. Clark, Secretary BUREAU OF MINES Robert C. Worton, Director Library of Congress Cataloging in Publication Data: Bremner, P, R. (Paul R,) A basic chloride method for extracting aluminum from clay. (Bureau of Mines report of investigations ; 8866) Bibliography: p. 8. Supt. of Docs. no.: I 28.23:8866. 1. Alumit~urn-Metallurgy. 2. Leaching. 3. Chlorides. 4, Kao- linite, I. Nicks, 1;. J. (Larry J.), 11. Bauer, D. J. (Donald J,). 111. Title. IV. Series: Report of investigations (United States. Bureau of TN23.U43 [TN776] 622s [669'.722] 84-600004 CONTENTS .Page Abstract ....................................................................... 1 Introduction ................................................................... 2 Materials. equipment. and procedures .......O.O...........,............... 3 Results and discussion........................................................b 3 Effects of calcination time and temperature .................................. 3 Single-stage leaching and crystallization... ................................. 4 Countercurrent leaching and crystallization.................................. 5 Purification and solubility studies ........................*................. 6 Thermal decomposition of ACHH ................................................ 7 Discussion and conclusions ............................................ 8 References ..................................................................... 8 ILLUSTRATIONS 1. Effects of clay calcination temperature .........................*.......... 4 2 . Single-stage leaching ........e........b............,..m......e....e......... 4 3. Test array for three-stage countercurrent leaching ......................... 5 TABLES 1. Composition of dried kaolinitic lay................^..............^...^... 3 2 . Summary of single-stage 30-pct AlG13 leaching ............................. 5 3 . Summary of countercurrent leaching results ................................. 6 4 . Impurity concentrations in cell-grade alumina and ACHH ..................... 7 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT OC degree Celsius mL milliliter pct percent wk week A BASIC CHLORIDE METHOD FOR EXTRACTING ALUMINUM FROM CLAY By Pe Re Bremner, Le Ja Nicks, and De JI ~auer~ ABSTRACT As part of a program to devise alternative technologies for producing alumina from domestic resources, the Bureau of Mines investigated the leaching of calcined kaolinitic clay to form basic aluminum chloride solutions. Bench-scale experiments were conducted for single-stage batch leaching with AlCl, solution and three-stage countercurrent leach- ing with substoichiometric HC1. Variable conditions of clay calcination and leaching were studied to determine their effects on aluminum extrac- tion and pregnant liquor composition. With clay calcined at the best temperature of a500 C, extraction of more than 93 pct of the aluminum was achieved. The basic chloride preg- nant liquors were crystallized and yielded the compound 5AlC1,-8Al(OH), -37.5H20, which can be thermally decomposed to alumina with 61.6 pct of the energy required for decomposition of A1C13*6H20. In comparison with the leaching operation in an HC1-clay process, the basic chloride system offers substantial advantages in energy consump- tion and equipment size requirements. -lMetallurgis t. 2~upervisoryresearch chemist. 3~upervisorychemical engineer. Reno Research Center, Bureau of Mines, Reno, NV. INTRODUCTION Almost all aluminum in the United In the HCl-clay process, kaolin is cal- States is produced from imported bauxite cined to an amorphous mixture of alumina or alumina. This country has, however, and silica, The calcined kaolin is more than adequate domestic nonbauxitic leached with HC1 solution, and aluminum alumina resources that could alleviate is dissolved according to the following dependency on foreign sources (11.4- For reaction: both economic and security reasons, the Federal Government has had a longstanding interest in the development of alterna- tive technology that would allow utiliza- The Al.C13 solution is evaporated or tion of those resources. sparged with HC1 gas, and the solid, A1C13*6H20, is formed. In 1927, the Bureau of Mines published a comparative study on extracting alu- During bench-scale research on KC1 minum from clay with sulfuric, nitric, leaching of calcined clay, sometimes the and hydrochloric acids (2). Alumina re- apparent extraction of h.1203 was greater search was resumed duriGg World War 11, than 100 pet, Examination of the data when the Defense Plant Corporation funded indicated that aluminum could be dis- four pilot plant studies (3) and the solved from kaolin with solutions con- National Bureau of Standards, under the taining less HC1 than required by reac- sponsorship of the Army Signal Corps, in- tion I. The resulting solutions con- vestigated an HC1 process for extracting tained basic aluminum chloride. alumina from kaolinitic clay (4).- A literature search revealed reports on In 1973, a program was initiated by the the solubility of A1(OH)3 and Alz03 in Bureau of Mnes to evaluate the technical solutions of AlClj (7). A study by and economic potential of several pro- Breuil (8) defined the compositions of cesses for producing alumina from domes- several ~?~stallinebasic aluminum chlo- tic resources (5). An HCl-clay process rides obtained by extended aging of mix- was judged the yest application of exist- tures of Al(OH)3, AlC13, and H20 at dif- ing technology (6). At the same time, ferent temperatures. bench-scale invesFigations were conducted on alternative technologies which might The formation of the basic chlorides of avoid some of the disadvantages of the aluminum may be represented by either of HC1 processes. the following reactions: A key operation in the HCl-clay process is the thermal decomposition of aluminum chloride hexahydrate (ACH) to the final alumina product. This step is energy in- tensive, and the viability of the process would be improved if the energy require- ment for decomposition was decreased. One possible way to achieve the decrease is to modify the process so that its where X + Tb = 3. Reaction 2 is a general aqueous operations did not produce ACH, expression for reaction 1 and leads to but a basic chloride with a composition the basic chloride when reactive A1203 is between ACH and alumina. in excess. men X is greater than 312, the coefficient for 820 becomes negative and water is consumed as the reaction $underlined numbers in parentheses re- proceeds to the right. Equation 3 ex- fer to items in the list of references at presses the direct reaction of AlC13 with the end of this report. A1203, which also consumes water. The value of Y is the molar ratio of C1:Al. The objectives of this study were to This ratio will be used as an determine the best C1:Al ratio for ex- indicator of composition, For example, tracting aluminum from calcined kaolin, C1:Al for ACH is three, for alumina it and to determine what, if any, basic alu- is zero, and the basic chlorides are minum chloride solids could be recovered intermediate. from the pregnant solution. MATERIALS, EQUIPMENT, AND PROCEDURES Raw clay was obtained from the Theile in a preheated electric furnace. After Kaolin Co., Sanderville, GA, and is rep- the specified time had elapsed, the cru- 1 resentative of very large deposits of cible was removed and allowed to air- eastern Georgia kaolinitic clay. The clay cool. For larger samples the clay was was dried for 48 h at 100" C, ground with roasted for 4 to 8 he a disk pulverizer to minus 60 mesh, and blended. Analysis by a combination of Leaching tests, both single-stage and wet-chemical methods and inductively countercurrent, were made in a 0.5-or 1-L coupled plasma emission spectroscopy gave glass resin kettle heated with an elec- the results shown in table 1. tric mantle and vented through a water- cooled condenser. The calcined clay TABLE 1. - Composition of dried charge and leaching solution were placed kaolinitic clay, percent in the kettle, heated to boiling, and stirred for the specified time. The test A1203...............ee.eee..e.... was terminated by vacuum filtration of Si02...............******.***.*** the hot contents of the kettle on a Buch- Ti02.e. .......................... ner funnel. The filter cake was washed Fe203............-.~~~~~~~~~~~~~~ with three 100 mL portions of water acid- K20.e.....meee...e.eee-*e0eee0-.0e ified to pH 3 with HC1. The combined P205..e.P..e.eeee.e*e**********I* filtrate and wash were evaporated to ,con- MgOs.e*..eeeeeeeeeeeeee-**oeeeeee centrate the contained aluminum salts, CaO..............e........ee.Ce~. At the first sign of crystallization, the hlaO..............e..e.....e...... liquor was allowed to cool at room tem- Total analyzed.............. perature overnight. The crystals were Theoretical hydrate H20. ......... filtered from the liquor, washed by slurrying in propanol, refiltered, and air-dried. The leach residue, combined filtrate, and crystals were analyzed for The dried clay was calcined prior to Al, C1, and the major impurities Fe, Mg, leaching. The calcined clay contained P, Ca, Na, and K. 41.1 pct A1203. In tests to determine the effects of