JOURNAL OF MATERIALS SCIENCE LETTERS 17 (1998) 27±29 Recovery of red iron oxide pigmentary powders from chemically- modi®ed steel-pickling chemical waste NASR E. FOUAD, HAMDY M. ISMAIL Chemistry Department, Faculty of Science, Minia University, El-Minia 61519, Egypt MOHAMED I. ZAKI Chemistry Department, Faculty of Science, University of Kuwait, P. O. Box 5969 Safat, 13060 Kuwait Steel-pickling chemical waste (SPW), which consists of 97.3% FeSO 4 ´7H 2 O [1], is produced following acid-washing of freshly manufactured steel sheets. A thermochemical investigation [1] has revealed that in atmospheres of air or dry O 2 SPW decomposes completely into red á-Fe 2 O 3 powders at > 700 8C, encompassing the release of the water of hydration at 100±240 8C and SO 2 at 500±600 8C. Physio-chemi- cal characterization studies [2] of the resulting iron oxide powders have disclosed that the application of high-temperature, or the non-oxidizing atmosphere of dry N 2 , facilitates particle growth, leading to a decrease in the red colour saturation and, conse- quently, the tinting strength. A quality red pigment was produced [2] on heating PSW at 700 8C for 5 h in an O 2 atmosphere. It has been recently found to 0261-8028 # 1998 Chapman & Hall 5 15 25 35 45 55 65 2θ, (deg) Intensity, (arbitrary units)→ 800 °C 700 ° 600 ° 500 ° 400 ° 300 ° 200 ° Original Figure 1 X-ray powder diffractograms (Ni-®ltered CuK á radiation) recorded using a model JSX-60 PA JEOL diffractometer for the original precipitate and its decomposition products obtained by heating in dry O 2 at 200±600 8C for 2 h, and at 700 8C and 800 8C for 5 h, (d) á-Fe 2 O 3 ASTM 33±664, (s) á-FeOOH ASTM 18±639, (3) Fe(OH) 3 ASTM 22±346. TABLE I Surface area (S BET ), speci®c gravity (r), average crystallite size ( D) and tinting strength (TS) for test pigments Pigment S BET a (2m 2 g 1 ) r b D c (2 nm) TS d (%) A(700)2 53 3.4 40 Ð A(700)5 35 3.9 35 94 A(700)10 42 4.9 45 Ð A(800)5 30 4.3 50 89 O(700)5 40 4.1 33 100 N(700)5 30 4.2 38 88 CP e 18 4.1 33 99 a Determined by BET-analysis [7] of N 2 adsorpotion isotherms d- etermined on the test samples at liquid N 2 temperature. The test samples were pre-outgassed at 120 8C and 6:6 3 10 3 Pa for 4 h. b Determined pycnometrically [8], using absolute ethyl alcohol as the immersion liquid. c Determined adopting the XRD line broadening technique [9]. d Determined using UV-VIS diffuse re¯ectance spectroscopy, and the method described by Kamel et al. [10]. e A commercial pigment supplied by the Paint and Industrial C- hemicals Co. (Cairo=Egypt). 5 15 25 35 45 55 65 2θ, (deg) Intensity, (arbitrary units) → N(700)5 A(700)5 O(700)5 Figure 2 X-ray powder diffractograms for the 700 8C decomposition products of the precipitate in air (á-Fe 2 O 3 ASTM 33±664), A(700)5, dry O 2 , O(700)5, and N 2 , N(700)5, atmospheres. 27