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| Fröhlich L., Fröhlichová M. |
| CHROME OCCURRENCE IN WASTES AND ITS STABILIZATIONIN THE PROCESS OF LIME SLAG SOLIDIFICATION |
Abstract
Original results of lime slag material research and the influence of additive (ferrous sulphate (FeSO4)) on the firmness of solidifying corpuscules and at the same time on chrome leachability of hardened corpuscules are published in the article.
The results of granulometric analysis of new lime slag decay originating in the production technology of rafining ferrochromes are published in the first part of the paper. The gained results show that up to 98,54 wt.% of slag is found in the particles from the interval of 0 to 0,2 mm. The substantial part of the slag mass is concentrated into a fine fraction of under 0,04 mm. Detailed laser method of particle size measuring showed that 90 wt.% of slag has the particle size of under 46,9 ?m. It was found out that the slag contained also superfine particles in the interval of 0 to 2 ?m. These superfine particles are necessary for the successful material solidification.
Ferochrome metal particles present in the slag have their share in the increase of total chrome content in the slag. By magnetic separation it was found out that they were concentrated into bigger, coarse grained particles of over 0,2 mm. They are not present in the fine fraction of under 0,04 mm. Their presence in the slag accounts for 10 wt.%. of total chrome presence. The chrome bound in the oxide form is present in the slag in two structural systems. They are structures of independent green particles of picrochromite - chrome spinel (MgCr2O4) and of particles of complex structures of system Ca-Si-Al-Mg-Cr-O with sexivalent (Cr6+) chrome. The chrome bond in the picrochromite is steady bond that does not decay by slag leaching in the water environment. The trivalent (Cr3+) chrome is not leachable. The picrochromite is harmless form of chrome in the slag. By the slag leaching, the Cr6+ is released from complex structures and passes into the solution. With the solidification, the Cr6+ has to be stabilzed, that is converted to an insoluble form.
The second part of the article presents the gained knowledge on the influence of stability aditive FeSO4 on the solidification process, mostly on the firmness of the formed corpuscules and on the chrome leachability in water after the hardening of solidification corpuscules. From the gained results it follows that already by adding small amount of additive up to 2,5 wt.% , 70% of leachable chrome (Cr6+) will be stabilized. At the same time the stabilized form`s firmness decreases by 43% of original firmness. Despite the fact, the achieved firmnesses are relatively acceptable; they reach values close to 16 MPa. By adding additive into the solidification mixture, the decrease of the bulk mass occurs as a result of micro-granules creation when blending the mixture. Hardening of such mixtures is accompanied by the porosity increase. When exceeding the optimum amount of additive, which is above 3 wt.% for FeSO4*4H2O, the solidification process is blocked and the firmness of the corpuscules is almost zero.
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| Keywords: wastes|alkaline activation|solidification|stabilization|chromium leaching| |
| No 2 (2004), p. 111-124 |
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| Híreš O. |
| IMPROVING OF FORGING DIES LIFE |
| Keywords: forging die|life improving|nitriding|refining|electro chemical treatment|facing|die hollow| |
| No 2 (2004), p. 125-131 |
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