7
Ind. Eng. Chem. Res. 1987,26, 7-11
ARTICLES
Domestic Saprolites as Potential Substitutes for Refractory-Grade Bauxite Jack C. White Albany Research Center, Bureau of Mines, United States Department of the Interior, Albany, Oregon 97321
T h e Bureau of Mines evaluated the potential for production of substitute refractory-grade bauxite (RGB) from saprolites and gibbsitic sands of the Southeastern United States. A statistical analysis of data from a reconnaissance sampling program indicates that the discovery potential in the Alabama Piedmont physiographic province for saprolites high in gibbsite is not encouraging. Furthermore, the -12-pm mineral concentrates produced from these saprolites and from gibbsitic sands of the Coastal Plain province were impure, contained insufficient alumina, and had poor refractory properties. A saprolite sample from the Valley and Ridge physiographic province was beneficiated by attrition scrubbing-hydrocycloning-wet high intensity magnetic separation t o provide a concentrate containing about 70% A1203with a pyrometric cone equivalent (PCE) of 35-36. Such material may be useful as a substitute for domestic 70% alumina bauxite based on the PCE values. More complete ceramic testing will be necessary t o confirm this tentative conclusion. Recovery of only about 10% of the original saprolite weight as a high-gibbsite concentrate indicates t h a t the proposed production method would be expensive compared with production costs in Guyana or China, the principal suppliers to the United States. T h e tonnage of saprolite suitable for production of a high-alumina substitute is still unknown. Refractory-grade bauxite (RGB), an imported commodity, has been utilized in the United States for formulating the high-alumina refractories essential to the steel, glass, cement, petroleum refining, and other industries. No deposita of refractory-grade bauxite are known to occur in the United States, and the possibility of such a discovery appears to be remote. Therefore, research was undertaken by the Bureau of Mines to investigate domestic aluminacontaining raw materials as potential substitutes for imported RGB. The principal supplier of RGB to the United States has been Guyana, a nation on the northeastern coast of South America. Interruption of the supply of Guyanese RGB during 1980, followed by depletion of refractories manufacturers’ stockpiles shortly thereafter, threatened a shutdown of manufacturing operations that utilize RGB. Fortunately, limited supplies of RGB from China became available in time to mitigate the effects of the shortage; however, nonuniformity in composition, difficulty in crushing the calcined RGB, and high-titanium content presented problems in the use of Chinese RGB. Recently, the composition of Chinese RGB has been more consistent, and its use is increasing. Because adequate supplies of Guyanese and Chinese RGB are now available, the United States continues to import them, making the United States almost as vulnerable to supply interruptions as before the temporary shortage. Specifications and Properties of Commercial Refractory-GradeBauxites. Extraordinarily high purity sets RGB apart from other bauxites, domestic or foreign. Guyanese RGB calcined to 1600 “C, known as RASC (refractory aggregate supercalcined), sets the standard for the industry (Table I).
Table I. Calculated RGB Specifications ( W )
constituent alumina, min iron oxide, max silica, max titania, max K 2 0 + Na20, max MgO + CaO, max LOI,” max
domestic bauxite 59.0 2.0 5.5 2.5 NDb ND ND
Guyana RASC 86.5 2.5 7.5 3.5 ND ND ND
national stockpile type I1 type I 86.5 86.5 2.5 2.5 7.0 7.0 4.0 3.75 0.2 0.5 0.5 0.3 0.5 0.5
“LO1 = loss on ignition. *ND = not determined.
Chinese bauxite is supplied in five grades containing nominally 85%, BO%, 75%, 60%, and 50% A1203. Refractory-grade bauxite specifications and chemical analyses presented by Wittmer (1982) in a recent survey paper are presented here for comparison with products made during this study (Tables I-IV). A comprehensive survey article on nonmetallurgical grades of bauxite was also published recently in Industrial Minerals (Harben and Dickson, 1983). Potential Domestic Alumina Sources. Potential domestic alumina sources are discussed briefly in the order presented in Table V. Purification of domestic bauxite by physical beneficiation or chemical processing is a conceptual route to an RGB substitute; however, the limited amount of available domestic bauxite, poor results of previous beneficiation and purification tests, and the large amount of research already done on domestic bauxites led to the conclusion that a different source material should be considered. The beneficiation of western kyanite has previously been investigated by the Bureau of Mines.
0888-5885/8712626-0007$01.50/0 0 1987 American Chemical Society
8 Ind. Eng. Chem. Res. Vol. 26, No. 1, 1987 Table 11. Chemical Compositions and Properties (Suppliers' Specifications)
constituent, % a 1u m in a iron oxide silica titania bulk density LOP PCEd
Guvana RASC 88.30 1.75 6.50 3.20 3.10 0.25 >40
85 87.50 1.50 6.00 3.75 3.10 0.20 38
Chinese grades" 80 84.50 1.50 6.50 4.00 2.80 0.20 38
" The term 'grades" refers to nominal A1203content, in percent. cone equivalent.
75 78.60 1.20 14.50 3.50 2.70 0.20 37
LO1 = loss on ignition.
Table 111. Chemical Composition of Bauxites (Bureau Analyses, % ) Chinese grades" shaft calcined 85 80 75 constituent Guyana RASC 87.8 80.9 75.1 alumina 89.0 0.19 1.30 2.27 iron oxide 1.76 silica 5.54 14.5 16.3 5.13 3.48 3.45 titania 3.47 3.85 0.12 0.14 0.34 0.02 CaO 0.18 0.08 0.12 0.006 KZO 0.09 0.09 0.10 0.007 MgO 0.04 0.05 ND' 0.03 NazO 0.00 0.08 0.00 0.10 LOP
domestic high-alumina grades 70 60 70.50 60.50 1.40 1.31 25.30 35.80 2.68 2.25 2.85 2.80 ND' ND 39 37 ND = not determined. dPCE = pyrometric
rotary calcined 85 80 89.8 82.0 2.96 2.98 4.08 10.1 4.14 3.83 0.10 0.21 0.56 0.24 0.10 0.08 0.06 0.07 0.00 0.00
domestic grades, calcined 70 60 70.9 66.7 1.70 2.05 21.4 27.8 3.49 3.11 0.03 0.08 0.01 0.06 0.04 0.07 ND 0.06 0.17 0.03
-
"The term "grade" refers to nominal A1203content, in percent. bLOI = loss on ignition. 'ND = not determined
Table IV. Mineralogy and Refractory Properties of Calcined Bauxites a-aludensity, mina Mullite PCE e/cm3 Chinese grades shaft calcined minor >40 3.68 85 major 37 3.44 minor-major major 80 minor-major 36 3.16 major 75 rotary calcined >40 3.74 major trace 85 3.52 major minor-major >40 80 domestic grades, calcined 39 3.16 trace major 70 ND" 37 3.15 major 60 minor >40 3.68 Guyana RASC major "ND = not determined.
Domestic kyanite is utilized for production of mullite refractories. However, kyanite is too high in silica to be used as an RGB substitute. A purified alumina substitute for RGB may be produced by chemical processing of kaolinitic clay, anorthosite, or alunite; however, the cost probably would be excessive in comparison with RGB, and such chemical industries would be vulnerable to reductions in the price of imported RGB. Dawsonitic Colorado oil shale was investigated by the Bureau of Mines as a source of Bayer-quality alumina (White et al., 1985). Two of the remaining potential domestic alumina resources, saprolite and gibbsitic sand, were selected as the subjects of this investigation, on the basis of their reported gibbsite content and extensive occurrence in the Southeastern United States. Saprolite, as defined by the American Geological Institute (1980), denotes "thoroughly decomposed rock formed in place by chemical weathering of igneous or metamorphic rocks." Bauxite may be defined as "an aggregate of aluminous minerals, more or less impure, in which aluminum is present as hydrated oxides." Bauxite forms by weathering under conditions favorable
Table V. Potential Domestic Sources of Alumina tons of material"/ ton of A1z03, formula % KzS04*Alz(S04)3* 37 4Al(OH)3 anorthosite Naz0~A1z03~6Si0z/CaO~27 A1,O3.2SiOZ NaAl(OH)$03 35 dawsonite 60 ferruginous bauxite complex A1z03~2Si0z~2Hz0 38 kaloinite AlZO3.SiOz 60 kyanite weathered rock 25 saprolite material alunite
" Assuming 100% extraction
2.7 3.7 2.9 1.6 2.6 1.6 4.0
efficiency.
for the retention of alumina and the leaching of other constituents. Gibbsite (Al20,-3H,O) is the most important alumina mineral of many bauxite deposits. The fundamental premise of this work was that saprolites or gibbsitic sand may contain gibbsite in a form that could be concentrated into an RGB substitute by means of physical mineral separation processes (beneficiation) (Murray and Walker, 1979; Murray and Iannicelli, 1982; Iannicelli, 1984).
Genesis and Occurrence of Gibbsite in Saprolites of the Southeastern United States The occurrence of aluminous saprolites containing gibbsite, as well as a summary of previous investigations of the gibbsite content of saprolites, is presented by Patterson (1967). Gibbsite Formation in the Valley and Ridge Physiographic Province. Gibbsite had been reported to occur in saprolites formed by rapid weathering of various source rocks in the Valley and Ridge physiographic province of the southern Appalachian region. The chemical mechanism of gibbsite formation there involves rapid groundwater leaching of alkalis, alkaline earths, and silica from aluminous source minerals, principally feldspars. Gibbsite
Ind. Eng. Chem. Res. Vol. 26, No. 1, 1987 9 Table VI. Sources of SamDles sample m e 1 saprolite 2 saprolite 3 gibbsitic sand 4 saprolite
physiographic province
location
Alabama Piedmont Alabama Piedmont Coastal Plain Valley and Ridge
Coosa county, A1 Coosa county, A1 Baldwin county, A1 Ennice, NC
site” A, B, A D
c
NA~
”Site A: road cut about 2.5 mi east of Pentonville, AL; SE1/4SE1/4 sec 8, T 21 N, R 19 E. Site B: road cut 2 mi east of Pentonville, AL; SE1/4SW1/4 sec 8, T 21 N, R 19 E. Site C: road cut about 0.5 mi SSE of Union Church, Al; W1/2SW1/4 sec 28, T 22 N, R 19 E. Site D: road cut 1-2 m below original surface; SE1/4SE1/4 sec 26, T 6 S, R 4 E. bNA = not available.
forms directly from feldspar in some areas, producing gibbsite pseudomorphs after feldspar. Conditions of good drainage and relatively steep slopes, where weathering is rapid, favor gibbsite formation by this mechanism in the deep saprolite zones (Calvert et al., 1980). In such areas, however, the soil and saprolite tends to be only a few feet thick. Gibbsite content of some soil horizons was reported to be as high as 40% (Cate and McCracken, 1972). In two detailed mineralogical and soils studies, Calvert et al. (1980) reported the formation of gibbsite from weathering feldspars in a deep saprolite horizon overlying granite. The gibbsite content on a whole-soil basis is low, probably less than 5%. Soil within 4 m of the surface contained almost no gibbsite because resilication converts gibbsite to the aluminosilicate clay mineral, halloysite. Conditions that favor formation of gibbsite in the deep saprolite zone also favor the chemical destruction of gibbsite by resilication in the near surface soils. An additional natural process that prevents accumulation of gibbsite on slopes is the slow and continuous downhill movement of unconsolidatedsoil materials (creep), with eventual removal by stream transportation. Unfortunately, the conditions that favor formation of gibbsite in saprolites of the Valley and Ridge province prevent the accumulation of gibbsite concentrations. During a recent parallel study on saprolites derived from basic rocks, no gibbsite was detected (Rice, 1981). Gibbsite genesis in saprolites of the Valley and Ridge province is in marked contrast to the accepted genesis of bauxite deposits wherein long-term weathering and desilication of aluminous minerals (laterization), including kaolinitic clays, form economic concentrations of alumina hydrate minerals (bauxite) (Patterson, 1967, pp 23-27). Gibbsite Formation in the Piedmont and Coastal Plain Physiographic Provinces. The chemical processes of norrnal bauxite formation probably explain the gibbsite content of saprolites on the relatively flat-lying Piedmont physiographic province and also the gibbsitic sands of the Coastal Plain provinces. In a soils study of the Alabama Piedmont province, Bryant and Dixon (1983) report the formation of gibbsite from quartz-mica schist. Although the gibbsite content of the clay fractions (material less than 2 pm) was as high as 30%, the clay fraction constitutes only a small part of the whole soil. Recalculation on a whole-soil basis indicates that the gibbsite content is about 10%. The calculated value is inexact because data on the silt size fraction (62.5-2 pm) was not provided. A reconnaissance study by the Alabama Geological Survey (Beg, 1982) determined the geographic distribution of gibbsite in saprolites of the east-central Alabama Piedmont province. From a statistical analysis of the survey’s data, it was determined that 79% of the 373 samples taken contained no detectable gibbsite, and most of the remaining samples contained less than 10% gibbsite (Figure 1). A second sampling was made of selected areas that were found to contain the highest gibbsite values. These areas were underlain by amphibolites. The data proved that most samples were also of low gibbsite content (Figure 2). The discovery
+
2 5
30 20 IO
0 0
F
0
I
I I 1 I 1 I 20 30 40 50 60 70 FREQUENCY OF GIBBSITE, CONTENT, pct
1
IO
0
I
80
Figure 1. Analysis of gibbsite content data of soil and saprolite samples from the east-central Alabama Piedmont province.
L 104 samples a
40
, i -
z
30
z k v)
m m -
20
IO O
W
ND
0
IO 20 30 FREQUENCY OF GIBBSITE CONTENT, pct
43
Figure 2. Analysis of gibbsite content data of soil and saprolite samples from selected high-gibbsite areas.
potential for high-gibbsite saprolites in this region is not encouraging. As a consequence of their low gibbsite content, preparation of an RGB substitute from these saprolites must involve separating a small amount of gibbsite from very large amounts of unwanted materials. The gibbsitic sands or soils of the Coastal Plain province were also investigated as a potential RGB substitute. Gibbsitic soils (defined as any soil containing greater than 6% gibbsite in the B and C horizons) presumably were formed by partial lateritic weathering of transported sediments. They extend in a broad belt from southern Mississippi into west-central Georgia (Clarke, 1971). The gibbsitic soil sample used in this study consisted of quartz sand in a matrix of iron-stained gibbsite and clay.
Experimentation and Results Samples and Sampling. To determine the possibility of producing high-purity gibbsite concentrates by physical beneficiation, three saprolite samples and one gibbsitic sand sample were investigated. The Alabama Piedmont samples, which were taken by the Bureau of Mines in cooperation with the Alabama Geological Survey, are believed to be representative of saprolite that is available in very large tonnage. Sample 1,a “composite” sample, received the greatest amount of work. Because of its pre-
10 Ind. Eng. Chem. Res. Vol. 26, No. 1, 1987 Table VII. Size Distribution of Sam& 1 weight gibbsite, % particle distribudiameter, mm g tion, % analysis distribution Wet Sieve Fractions 10.40 82.52 20.71 2.2 +1.000 1.20 20.90 5.25 1.0 -1.000 + 0.710 1.76 -0.710 + 0.500 20.50 5.15 1.5 2.25 28.06 7.04 1.4 -0.500 + 0.355 2.41 21.13 7.53 1.4 -0.355 + 0.250 37.26 9.35 1.7 3.63 -0.250 + 0.180 27.30 6.85 2.3 -0.180 + 0.125 3.60 20.64 5.18 2.4 -0.125 + 0.090 2.84 5.82 16.66 4.18 6.1 -0.090 + 0.063 19.53 4.90 6.7 7.50 -0.063 + 0.045 ~
+0.045 -0.045 + 0.033 -0.033 + 0.024 -0.024 + 0.017 -0.017 + 0.013 -0.013
Hydrocyclone Fractions 0.033 0 0.13 2.06 0.52 3.6 13.6 8.32 2.09 2.82 17.5 11.23 2.03 13.8 8.09 16.36 9.1 65.19
a 0.43 6.49 11.27 6.39 34.00
Below limits of detection.
sumed high-gibbsite content, sample 2 was processed separately and reported as the “selected” sample. Sources of the four samples are given in Table VI. Sampling was intended to provide research data for producing an RGB substitute. The purpose was not to delineate a potential gibbsitic resource amenable to beneficiation. Characterization and Physical Beneficiation. The four samples were prepared by attrition scrubbing a dense slurry of cake-batter-like consistency for 5 min to clean the particle surfaces and break up the clay balls. Size fractions were produced by wet and dry sieving and by hydrocycloning of the -45-pm subsieve fraction. Five subsieve size fractions were produced by a multiple-series cyclone separator. Size fractions produced in this manner were analyzed by a number of methods including petrographic examination, wet chemistry, X-ray diffraction, and differential scanning calorimetry (DSC). Differential scanning calorimetry is an instrumental thermal analytical method whereby enthalpy changes are quantitatively determined during heating of sample materials. The gibbsite content of unknown samples was determined by the enthalpy change during the loss of water of crystallization. Water loss from other hydrated aluminosilicate minerals in the samples, such as kaolinite, occurred at different temperatures and therefore did not interfere with the gibbsite determinations. All gibbsite analyses were performed by DSC because X-ray diffraction proved to be unsatisfactory. Petrographic examination of samples 1 , 2 , and 4 demonstrated that the coarse size fractions consist of partly weathered rock and mineral fragments consisting mostly of quartz, feldspar, and micas. Because of the similarity between samples 1 and 2, sample 2 was not investigated in detail. Petrographic examination of sample 3 determined that the size fractions consisted essentially of angular to subangular quartz grains. Minor amounts of microcline were reported by X-ray diffraction in a few of the finer size fractions. Attrition scrubbing had removed most of the red iron-stained matrix from the quartz grains. All size fractions were analyzed for gibbsite by DSC. No other alumina hydrate minerals were detected by either DSC or X-ray diffraction. The distribution of gibbsite throughout the various size fractions of three samples is presented in Tables VII-IX. The data prove that gibbsite is present in significant amounts only in the subcyclone
Table VIII. Size Distribution of SamDle 3 weight particle distribugibbsite, 7a diameter, mm g tion, % analysis distribution Wet Sieve Fractions +LOO0 28.82 6.30 0.9 0.35 -1.000 + 0.710 21.14 4.62 0.3 0.09 0.11 -0.710 + 0.500 39.30 8.59 0.2 0.36 -0.500 + 0.355 65.60 14.34 0.4 -0.355 + 0.250 48.52 10.60 0.3 0.20 -0.250 + 0.180 34.23 7.48 0.5 0.23 -0.180 + 0.125 25.61 5.60 0.6 0.21 -0.125 + 0.090 16.39 3.58 0.9 0.20 2.49 1.6 -0.090 + 0.063 11.40 0.25 -0.063 + 0.045 8.62 1.88 2.4 0.28 +0.045 -0.045 + 0.033 -0.033 + 0.024 -0.024 + 0.017 -0.017 + 0.014 -0.014
Hydrocyclone Fractions 0.26 0.06 a 2.55 0.56 2.5 4.64 1.01 6.6 4.37 0.96 10.5 3.10 0.68 13.6 143.0 31.25 49.5
a 0.01
0.41 0.63 0.57 96.10
Below limits of detection.
Table IX. Size Distribution of Sample 4 weight ______ gibbsite, % particle distribug tion, 70 analysis distribution diameter, mm Wet Sieve Fractions +2.0 4.43 0.92 0.3 0.04 -2.0 + 1.7 2.26 0.47 0.5 0.03 -1.7 + 1.0 12.12 2.51 0.7 0.24 -1.0 + 0.710 13.44 2.78 0.9 0.34 4.70 1.2 0.77 22.69 -0.710 + 0.500 8.65 1.1 1.30 -0.500 + 0.355 41.76 52.57 10.89 1.3 1.94 -0.355 + 0.250 69.67 14.44 0.8 1.58 -0.250 + 0.180 -0.180 + 0.125 73.46 15.22 0.7 1.46 -0.125 + 0.090 53.75 11.14 0.8 1.22 -0.090 + 0.063 32.75 6.79 0.9 0.84 -0.063 + 0.045 26.26 5.44 0.9 0.67 +0.040 -0.040 + 0.030 -0.030 0.021 -0.021 0.015 -0.015 0.012 -0.012
+ + +
Hydrocyclone Fractions 2.75 0.57 0.2 5.90 1.22 0.6 5.23 1.08 2.3 4.02 0.83 6.1 2.8 0.58 11.5 56.77 11.76 54.3
0.02 0.10 0.34 0.69 0.91 87.49
fractions (-12 lm). The subcyclone fraction of sample 1 and sample 2 contained 9% and 28% gibbsite, respectively, whereas, the subcyclone fractions of sample 3 and sample 4 contained 49% and 54% gibbsite, respectively (Table X). Samples 1 and 2 are of no interest as a substitute for RGB because of the low gibbsite content of the subcyclone fractions. Samples 3 and 4 were investigated further. Wet highintensity magnetic (WHIM) separations were made of the two materials. When a l/s-in. steel ball matrix was used, little or no magnetic concentrate was produced from the gibbsitic sand subcyclone fraction even though this fraction contains 30% Fe203on a calcined basis. WHIM separation at 10 kG with a coarse steel wool matrix produced a magnetic concentrate equal to almost half the sample weight but with very poor iron-aluminum separation. The inability to separate the very large amount of iron in the sample correlates with the fact that no iron mineral was detected by X-ray diffraction, indicating very fine particle size. On the basis of this sample, gibbsitic sand is not a potential source of an RGB substitute that can be produced by physical beneficiation.
Ind. Eng. Chem. Res. Vol. 26, No. 1, 1987 11 Table X. Analyses and Physical Properties of the Subcyclone Fractions of Saprolites and Gibbsitic Sand Compared with Domestic Bauxite chemical analyses, % samples A1203 SiOz FeZ03 TiOz (Na + K)20 gibbsite, % PCE saprolites sample 1 41 42 9.6 1.7 1.5 9 26 sample 2 52 34 10 0.80 1.1 28 33 ND” ND ND sample 4 ND ND 54 ND 65-71 17-22 4-5 ND ND 58-62 sample 4b 35-36 gibbsitic sand: sample 3 49 22 30 2.2 0.22 49 26 domestic 70 grade bauxite 71 21 1.7 3.5 ND ND 38-39 ND = not determined.
Wet high-intensity magnetic separation (WHIM).
The only sample of potential interest is sample 4. The concentrate produced by hydrocycloning and WHIM separation contained about 60% gibbsite, with the remaining 40% consisting essentially of kaolinite with traces of muscovite and quartz, as determined by DSC and X-ray diffraction. About 10% of the original sample weight was recovered as product. Further upgrading by physical beneficiation is not considered to be practical because of the very fine grain size of the concentrate (-12 pm). The chemical analyses and PCE values of the concentrates, as compared with domestic “70 grade” bauxite, are presented in Table X. The pyrometric cone equivalence test (ASTM C24) is a physical testing method whereby a specific thermal deformation characteristic of a ceramic material may be determined, during heating to high temperatures, in comparison to a similar characteristic for standard materials. Alumina contents and PCE values demonstrate that the only concentrate approaching the refractory properties of 70 grade domestic bauxite is the sample 4 subcyclone fraction upgraded by WHIM separation. The sample 4 concentrate contains about 70 pct A1203on a calcined basis and has a PCE value of 35-36. None of the concentrates were suitable as substitutes for RGB.
Discussion The possibilities for mineral separations that could produce RGB substitutes from the saprolites investigated herein appear to be limited to size separation and WHIM separations. The separation of other minerals such as quartz, feldspar, mica, and kaolinite, from gibbsite in very fine particle sizes is probably beyond the capability of present technology. Of these minerals, kaolinite is the only acceptable diluent in gibbsite concentrates. Data presented by Calvert et al. (1980, p 1100) are significant with regard to the mixtures of minerals to be expected in the subcyclone fractions. In Calvert’s study, no size fraction of any soil horizon consists entirely of gibbsite, although a few clay fractions (-2-pm material) contain about 80% gibbsite. The -12-pm subcyclone fractions however, also include the finest silt fractions (-12 2 pm), which consist, in part, of the unwanted minerals mica, feldspar, and quartz. Consequently, the subcyclone fractions are of lower grade than the reported clay fractions. Attrition scrubbing will abrade the coarse minerals, producing additional unwanted fines. Optimum attrition scrubbing of saprolites containing mostly gibbsite and kaolinite in the subcyclone fraction appears to be the only
+
effective approach to production of an acceptable cyclone feed. The availability of such saprolites has not been determined. Cyclone sizing during this study was done in a laboratory separator that provides extraordinarily complete size separations for accurate characterization work. Industrial separations, however, would not be as perfect, indicating that some degradation of product quality may occur.
Conclusions 1. The discovery potential for Alabama saprolites from which RGB substitutes may be prepared seems to be poor. 2. Should such a saprolite discovery be made or should the North Carolina saprolite prove to be an acceptable raw material, the cost of extraction would be high because of the low gibbsite content. 3. Investigation of the refractory properties such as hot modulus of rupture of the North Carolina concentrate is required to determine its possible use as a substitute for 70% alumina bauxite. Registry No. Gibbsite, 14762-49-3; Bauxite, 1318-16-7.
Literature Cited Glossary of Geology; American Geological Institute: Fair Chucke, VA, 1980; p 556. Beg, M. A. Circ.-Geol. Surv. Ala. 1982(Apr),77. Bryant, J. P.; Dixon, J. B. Presented at the Proceedings of the 12th National Conference on Clays and Clay Minerals, Atlanta, GA, Sept-Oct 1963; pp 509-521. Calvert, C. S.; Buol, S. W.; Weed, S. B. Soil Sci. SOC.Am. J. 1980, 44(5), 1096-11 12. Cate, R. B.; McCracken, R. J. Southeast. Geol. 1972,14(2),107-112. Clarke, 0. M. Southeast. Geol. 1971, 13(2), 77-90. Harben, P.; Dickson, T. Znd. Miner. (London) 1983, 192, 25-43. Iannicelli, J. Presented a t the Proceedings of the 1984 Bauxite Symposium, Los Angeles, Feb 27-March 1, 1984; pp 681-689. Murray, H. H.; Iannicelli, J. Technical Report NSF/RA-800286, pp 24-32, 1982; National Bureau of Mines, Washington, DC. Murray, H. H.; Walker, S. Trau. ZSCOBA 1979, 15, 143-150. Patterson, S. H. US.Geol. Suru. Bull. 1967, 1228, 176. Rice, T. J., Jr. Ph.D. Thesis, North Carolina State Universitv, “ . Raleigh, 1981; p 235. White, J. C.; Mauser, J. E.; Henry, J. L. Presented at the 18th Oil Shale Symposium Proceedings, Grand Junction, CO, 1985; pp 182-195. - - - - - -. Wittmer, D. E. Presented at the AIME Proceedings of the Light Metals Sessions, Feb 1982; pp 23-35. Receiued for reuiew December 14, 1984 Revised manuscript received July 21, 1986 Accepted August 22, 1986
