GB1574974A - Blast furnace and a process for recovering noble metals - Google Patents

Description

(54) A BLAST FURNACE AND A PROCESS FOR RECOVERING NOBLE METALS (71) We, DEUTSCHE GOLD-UND SILBER SCHEIDEANSTALT VORMALS ROESSLER, a body corporate organised under the laws of Germany of 9 Weissfrauenstrasse, 6 Frankfurt Main 1, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the methode by which it.is to be performed, to be particularly described described in an by the following statement: This invention relates to a blast furnace for the recovery of noble metals from waste products containing noble metals, and to a special process for such recovery.

A large proportion of the noble metal used in industry, research, etc., is subjected as waste product to a smelting process for the purposes of recovery. The waste products in question are in the form of metallic waste containing noble metals ("separation stop") and noble metals accompanied by nonmetallic materials ("dross"). These waste products are normally smelted in a blast furnace.

Together with the coke used as energy carrier and reducing agent, the lead oxide as noble metal collector and other slag formers such as, for example, limestone, pyrites cinders and sand, the noble-metal-containing waste products form the blast furnace input which is then melted down together. The blast furnace products formed in this way include work lead containing, on average, 50% of lead, 20% of copper, 25% of noble metal and 5% of iron and nickel, low-grade matte (a copper-iron-sulphur compound), slag and the fly dust of the waste gas.

The molten blast furnace products are tapped at two levels. The mixed phase of higher specific gravity, consisting of low-grade matte and work lead, is tapped into ingots from the lower part of the blast furnace, the so-called sump. The two phases then separate by virtue of their different specific gravities and, after solidification, are separated from one another. The noble-metal-containing work lead is further processed, whilst the considerably lighter, molten slag is run off from the blast furnace above the metal tapping zone.

The amount of air required for burning the coke is injected into the blast furnace by means of tuyeres uniformly distributed over the circumference of the furnance. Permeability to air and the height of the charging column control blast volume and pressure. The melting temperature, the working of the furnace (melting behaviour) and throughput are critically determined by the blast volume and temperature. Poor or non-uniform permeability to air promote encrustation in the blast furnace through the deposition of the slag, especially in the vicinity of the tuyeres, which results in further deterioration of the furnace process by narrowing the cross-section of the furnace.Added to this is the relatively high noble metal content of the slag because, with a reduced furnace cross-section and an asymmetrical distribution of temperature, there is neither sufficient time nor sufficient space for completely liquating the noble metals into the work lead.

On account of these difficulties and the damage arising out of them, the mode of operation and working of conventional blast furnaces is extremely unsatisfactory.

Accordingly, an object of the present invention is to increase the throughput of a blast furnace for the same or better product quality (slag poor in noble metals), to stabilise the furnace process inter alia a good separation of the melt phases) and to obtain a simpler and safer method of operation.

According to the invention, this object is achieved by virtue of the fact that the lower part of the blast furnace is widened cylindrically relative to the upper part by 25 to 100% of the remaining furnace cross-section over at least 25% of the furnace circumference beyond the entire cross sectional area of the furnace.

The present invention relates to a blast furnace for obtaining noble metals from waste products containing noble metals, with the addition of coke and slag formers, the blast furnace consisting essentially of an upper part and a lower part, wherein the lower part is widened cylindrically relative to the upper part over at least 25% of the furnace circumference up to over the entire furnace circumference by 25 to 100% of the cross-section of the furnace and all of the tuyeres which supply only air are located in the lower part of the blast furnace, and above the line of impact of the bulk material inside the furnace on the furnace wall.

The increase in cross-section preferably amounts to from 40 to 70% because the best results are obtained in this region. Hitherto, the lower part of the blast furnace, the so-called sump, has always has the same or even a smaller cross-sectional surface than the blast furnace itself, as measured at the junction between the sump and the upper part of the blast furnace.

All of the tuyeres are situated in the lower part of the blast furnace (sump) in the upper section thereof above the line along which the bulk material (i.e. the mixture of waste products containing noble metal, coke and additives) impinges on the wall of the furnace.

The arrangement and number of tapping possibilities for the removal of metal and slag on the circumference of the sump'its arbitrary, although it should preferably be situated outside the charging and melting zone. The slag tapping zone above all is with advantage situated outside the charging and melting zone, because in this way particles containing noble metal are prevented from passing directly to the tap hole and hence from being discharged with the slag.

On account of the tuyeres shifted outwards by the widened lower section, an annular cavity is formed under the effect of the cone of the charge. An advantageous heat absorption of the blast is thus obtained in this zone. In other words, the blast undergoes secondary preheating between the tuyeres and the charging column.

This indirect preheating of the blast provides for better utilisation of energy, for a more uniform temperature profile in the blast furnace through the equalisation of temperature in the tuyere plane, for the avoidance of high top heat through displacement of the combustion zone into the lower part of the furnace, for the prevention of slag encrustation through higher combustion temperatures in front of and above the tuyeres, which enables the tuyeres to be kept open more effectively and facilitates manual cleaning of the tuyeres, and ensures an unimpeded blast passage at a low air-blast velocity for high blast volumes.

In addition to preheating the blast and equalising temperature, the formation of this annular cavity is significant for another very important reason which is that this cavity acts as a pressure equalising zone, in other words a uniform pressure prevails across the furnace cross section. The formation of blowholes is prevented. In addition, the uniform flow through the entire charging column due to the increase in the reaction surface contributes towards accelerating the chemical reactions.

The discharge of fines is also reduced by the filter effect of the charge.

The novel construction of the lower part of the blast furnace influences not only the furnace process and output, but also the quality of the products are reflected in particular in a slag of very low noble metal content.

An object is to reduce the noble metal contents of the slag to such an extent that it may be discarded and does not, as return feed, impose an additional load upon the blast furnace, thereby indirectly increasing costs.

This object is achieved by continuously tapping the slag which regularises and stabilises the entire melting zone. The slag tapping zone is situated above the metal and slag constituents entering the melting zone. The slag is thus forced to ascend towards the tap hole. By virtue of this long, upwardly directed path of the liquid slag, the heavy metal particles are liquated and are deposited in the sump.

One example of embodiment of the blast furnace according to the invention is described in the following with reference to the accompanying drawing.

A blast furnace 20 consists of a refractorily lined, cylindrical shaft 1 which tapers downwards in a refractorily lined cone 2 supporting a charging column with a coke skeleton 3 (i.e.

a skeleton of unspent coke within the charging column which remains in the furnace after the metal and the slag melt out since the coke cannot melt). The conical part is adjoined by another cylindrical part which consists of water jackets 4. The water is fed in from below at 5 and run off at the highest point 6 in order to prevent the formation of air bubbles and, hence, destruction of the water jackets 4.

The water jackets 4 are adjoined in the downward direction by a lower part 19 of the blast furnace 20 which, in this case, is widened over the entire cross-section. Tuyeres 7 are also arranged in this zone. The angle of slope of light coke 8 provides for the formation of an annular cavity 9 used for preheating.

Below this lower section 19 of the blast furnace is situated a so-called refractorily lined "sump" 10 which is used for receiving the liquid phase. By virtue of the specific gravities, this liquid phase consists of three layers, namely a heavy metal phase at the bottom 11, an overlying low-grade matte phase 12 and, on top, a light slag phase 13.

Descending metal 14 is run off through a tap hole 15. Slag permeated with drops of metal initially sinks down, the metal precipitates 14 whilst the slag, now ascending free from metal 16, leaves the sump continuously through a tap hole 17, a metering unit 18 regulating the quantity of slag.

WHAT WE CLAIM IS: 1. A blast furnace for obtaining noble metals from waste products containing noble metals, with the addition of coke and slag formers, the blast furnace consisting essentially of an upper part and a lower part, wherein the lower part is widened cylindrically relative to the upper part over at least 25% of the furnace circumference up to over the entire furnace circumference by 25 to 100% of the crosssection of the furnace and all of the tuyeres which supply only air are located in the lower part of the blast furnace, and above the line of impact of the bulk material inside the furnace on the furnace wall.

2. A blast furnace as claimed in Claim 1, wherein the increase in cross-section amounts to from 40 to 70%.

3. A blast furnace for recovering noble metals from waste products containing noble metals substantially as described with particular reference to the accompanying drawing.

4. A process for recovering noble metals from waste products containing noble metals using a blast furnace as claimed in any of Claims 1 to 3, wherein the slag is continuously tapped from the blast furnace.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. whilst the slag, now ascending free from metal 16, leaves the sump continuously through a tap hole 17, a metering unit 18 regulating the quantity of slag. WHAT WE CLAIM IS:

1. A blast furnace for obtaining noble metals from waste products containing noble metals, with the addition of coke and slag formers, the blast furnace consisting essentially of an upper part and a lower part, wherein the lower part is widened cylindrically relative to the upper part over at least 25% of the furnace circumference up to over the entire furnace circumference by 25 to 100% of the crosssection of the furnace and all of the tuyeres which supply only air are located in the lower part of the blast furnace, and above the line of impact of the bulk material inside the furnace on the furnace wall.

2. A blast furnace as claimed in Claim 1, wherein the increase in cross-section amounts to from 40 to 70%.

3. A blast furnace for recovering noble metals from waste products containing noble metals substantially as described with particular reference to the accompanying drawing.

4. A process for recovering noble metals from waste products containing noble metals using a blast furnace as claimed in any of Claims 1 to 3, wherein the slag is continuously tapped from the blast furnace.