Conversion of Red Muds into Pozzolans.
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CONVERSION OF RED MUDS INTO POZZOLANS.
JEAN PERA Laboratoire des Mat6riaux Min6raux, Bat. 407, INSA de Lyon, Avenue Albert Einstein, 69621 VILLEURBANNE Cedex, FRANCE.
20,
ABSTRACT Red muds are waste materials obtained from the aluminium extraction industry. They consist mainly of clays, aluminium and iron hydrated oxides. Three muds were studied; they differed in chemical and mineralogical compositions. They were converted into reactive pozzolans by calcination in the temperatu0 re range 600-800 C for five hours. Pozzolanicity was investigated on calcined red mud-OPC mixes studying strength development and lime consumption as evaluated by DTA. The nature of hydrates formed during hardening was also identified. The mineralogical composition of the mud is the most important factor affecting its pozzolanicity. Blended cements containing 30% calcined red mud develop significant strengths. INTRODUCTION Red muds are by-products of the aluminium industry. They consist mainly of oxides and hydroxides of silicon, aluminium, iron and calcium. Their compositions vary with the raw material used for the production of aluminium metal. In order to investigate the possibility of using such wastes as additives in the cement industry, tests were carried out to examine the pozzolanic properties of calcined red muds. Three muds were chosen: two of them mainly contained boehmite, gibbsite, and hematite; the other contained kaolinite, hematite, and calcite. After calcination in the range 600800C, kaolinite is converted to a pozzolan [1-4). Gibbsite and boehmite generally decompose, at about 2OO-350°C [5]. During calcination, a disorganization in the crystal structure occurs and is responsible for a high reactivity with lime in the presence of water. EXPERIMENTAL Chemical and Mineralogical Analysis of Red Muds. Chemical compositions and physical properties of the red muds are given in Table 1. The particle size distribution was measured using a laser granulometer MALVERN 2200/3300.
Mat. Res. Soc. Symp. Proc. Vol. 245. @1992 Materials Research Society
56
Table 1.
Chemical analysis and physical muds used.
properties of the
Red Mud N' Composition and physical properties Oxides (% by mass) Si02 A1203 Fe203 MgO CaO Na20 K20 Ti02 P205
1
2
3
10.2 27.3 19.4 0.7 8.6 5.2 0.3
3.7 21.1 56.0 0.1 0.2 0.4 0.1
9.2 14.2 41.6 1.4 12.0 3.3 0.1
11.4 16.5 10
0.8 15.7 17
6.6 11.8 21
2.5
2.8
2.6
80 45 25
70 40 20
100 80 60
8
10
25
1.9 0.3
C02 Loss on ignition Specific surface area (B.E.T) m2/g Density (g/cm3) Size - distribution passing 64 im(%) 16 pm(%) 4 pm(%) 1 pm(%)
2.3 0.4
3.8 1.0
Table 2 shows information on the mineralogical analysis which was both assessed by X-ray diffractometry and I.R. spectrometry. Table 2.
Minerals present in the muds. Mud N'
Minerals 3
12 Anatase Boehmite Calcite
x x x
x
x x
Gibbsite
x
x
x
Goethite Hematite
x
Kaolinite
x x
x x
_
Cement The cement used was an ordinary portland cement (OPC), Class 55 according to French standards. Its Bogue potential composition was : C3 S = 57% ; C
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