Mill scale briquetting

Abstract

The invention relates to a method of agglomerating iron oxide-containing residual substances, in particular scale and mill scale, wherein the residual materials and the paper sludge are dried and comminuted and agglomerates are produced by means of hot briquetting from the mixture comprising the residual substances and the paper sludge. In this way, mill scale briquettes of high strength and density can be produced which in steelmaking processes can then be charged into an electric arc furnace for the purpose of recycling the iron contained in the residual substances.

Claims

1. Method for the agglomeration of iron oxide-containing residual substances by means of which paper sludge is comminuted and, optionally, the residual substances are comminuted, and a mixture of residual substances, either having a residual substance water content of less than 5% by weight or dried to a water content less than 5% by weight, and dry paper sludge dried to a water content of less than 5% by weight, is briquetted at a temperature ranging between 70 and 350 C., wherein the mixture contains 15 to 35% by weight of dry paper sludge and wherein material selected from the group consisting of steel shavings, cast-material swarf, metal-containing steel mill residual material and metal-containing composite packing material are added to the mixture.

2. Method according to claim 1, characterized in that the iron oxide-containing residual substances are, at least in part, scale or mill scale.

3. Method according to claim 1, characterized in that the mixture contains 50 to 95% by weight of residual substances.

4. Method according to claim 1, characterized in that the size reduction is carried out simultaneously with mixing of the residual substances and the paper sludge in a ball mill or vibratory mill.

5. Method according to claim 4, characterized in that cylindrical bodies are used as grinding elements for the size reduction of the residual substances and the paper sludge.

6. Method according to claim 4, characterized in that a drying and/or preheating of the mixture is additionally carried out in the ball mill or vibratory mill.

7. Method according to claim 1, characterized in that briquetting is performed at a temperature ranging between 90 and 250 C.

8. Method according to claim 1, characterized in that briquetting is performed at a pressure ranging between 10 and 500 MPa, preferably between 30 and 350 MPa and particularly preferred between 100 and 200 MPa.

9. Method according to claim 1, characterized in that material selected from the group consisting of aluminum, copper, manganese, magnesium, silicon, silicon carbide, ferrochrome, ferromanganese, ferrophosphorus, ferrosilicon, ferrosilicon magnesium, ferrotitanium, chrome, nickel, ferronickel, molybdenum, ferromolybdenum, cobalt, ferrocobalt, zinc oxide, zirconium, tungsten, vanadium and steel powder are added to the mixture.

10. Method according to claim 1 or 2, characterized in that the mixture contains 65 to 85% by weight of residual substances.

11. Method according to claim 1, characterized in that briquetting is performed at a temperature ranging between 90 and 150 C.

Description

(1) Embodiment Example

(2) Mill scale (water content: 5% w/w) and paper sludge (water content: 57% w/w) were dried for a period of 24 hours in a drying cabinet at a temperature of 85 C. In this manner, the water content was lowered to less than 5% w/w in each case. After drying, the paper sludge had a flaky consistency with its grain size being less than 20 mm.

(3) Following this, the mill scale, flaky paper sludge and a small amount of steel shavings were mixed at a ratio of 79:20:1% w/w and comminuted by means of a ball mill such that mill scale and paper sludge particles were produced the grain size of which was below 1 mm for 90% w/w of each of the constituents.

(4) For hot briquetting purposes, the mixture was then charged into a cylindrical die. Briquetting was carried out at a pressure of 150 MPa and a temperature of 140 C. The strength (splitting tensile strength) of the briquettes produced in this manner was verified by means of the Brazilian test. The briquettes so produced had a strength of 3.2 MPa and a density of >2.5 g/cm.sup.3.

(5) High-Temperature Strength

(6) To investigate the strength characteristics the above mentioned briquettes were tested under high-temperature conditions. When subjected to a pressure load of 1 MPa the briquettes maintained their original shape up to a temperature of approx. 1000 C. At higher temperatures the briquette suffered deformation but kept its integrity as an agglomerate which means there was no dust formation and the valuable iron constituents were capable of entering the deeper zone of the metallurgical reactor.

(7) Melting Behavior

(8) The produced briquettes (800 g) and steel blocks C45 (4000 g) were heated and melted in an induction furnace. The briquettes endured the heating process. The iron oxide was reduced to form metallic iron and dissolved in the metal bath. The melt was then poured into and cooled down in a casting die. The composition of the cast metal block did not show increased proportions of undesirable elements (e.g. sulfur, copper, tin).