GB2188943A

GB2188943A - Removing arsenic from speisses

Info

Publication number: GB2188943A
Application number: GB8608678A
Authority: GB
Inventors: J Hood; J A Litten; P Halsall
Original assignee: CAPPER PASS Ltd
Current assignee: CAPPER PASS Ltd
Priority date: 1986-04-09
Filing date: 1986-04-09
Publication date: 1987-10-14
Also published as: GB2188943B; GB8608678D0

Abstract

A process for removing arsenic from solid furnace products, especially speisses, involves fluidising particulate solids in an oxygen-containing gas, in the presence of a sulphur source such as pyrites or elemental sulphur or employing SO2 as the fluidizing gas. The arsenic is fumed off as arsenic sulphide and is collected from the gas stream leaving the fluidised bed.

Description

SPECIFICATION A method of removing arsenic from solid pyrometallurgical products This invention relates to a method of removing arsenic from pyrometallurgical products produced during the smelting of non-ferrous metals and more especially to the removal of arsenic from speisses.

In the smelting of complex materials containing e.g. tin, lead, copper with arsenic and iron, a compound of iron and arsenic called 'speiss', holding minor amounts of other nonferrous metals, separates as a less-dense layer in the furnace-ladle or forehearth. It is common practice to augment the iron in the charge to capture as much arsenic as possible-though this also incurs the loss of valuable metals, for instance, tin and precious metals. The iron-arsenic phase can contain up to 30% arsenic in the most favourable cases.

Many smelters have for long regarded this speiss as the most suitable material for longterm disposal of arsenic by dumping, but the valuable metal contents are sometimes too high for dumping, and there is now doubt about the long-term stability of speisses.

It is an object of this invention to remove arsenic from such products as speisses in a highly-efficient manner, to leave a residue substantially free of arsenic, and to produce a concentrated arsenic-containing solid for disposal by encapsulation or dumping or suitable for working-up into valuable arsenic compounds.

This invention consists in a process for removing arsenic from a particulate arsenic containing solid, comprising heating the solid either in the presence of a sulphur source in an oxygen-containing gas stream or in a stream of a sulphur dioxide-containing gas, and fuming off arsenic sulphide in the gas stream.

Preferably the oxygen-containing or S02-containing gas is employed to fluidise the particles of arsenic-containing solid.

Preferably the sulphur source is selected from pyrites, elemental sulphur and metal sulphide concentrates.

Preferably the arsenic-containing solid is a speiss.

Preferably the oxygen in the gas is insufficient to convert all the sulphur in the sulphursource to sulphur dioxide.

Preferably the temperature within the reactor is within the range of 500"-900"C.

The invention will now be further described and illustrated by reference to the following non-limiting Examples.

EXAMPLE I Tests were conducted using a tube furnace operating at 800"C.

a. In the first test a mixture of speiss and pyrite were heated together whilst a stream of air was passed through the tube. This produced a calcine containing 0.63% As and represented 93.85% removal of the arsenic.

b. In the second test a similar mixture was heated in the same way but a stream of pure nitrogen was passed through the tube. The calcine produced in this case contained 10.01% As representing little or no removal of the arsenic.

c. A third test was carried out using speiss alone and a stream of pure sulphur dioxide was passed through the tube. The calcine produced contained 0.21 % As, representing 98.22% removal of the arsenic.

So from test 'a' we deduce that.volatile arsenic sulphide is produced either from intimate contact between the speiss and the iron pyrites or from sulphur dioxide produced as the pyrite is burnt in the air stream.

Test 'b' eliminates the former and test 'c' substantiates the latter.

EXAMPLE 2 Using a 6" diameter pilot scale fluid bed reactor the following results were obtained for certain mixtures of speiss and sulphur containing reagent. The effect of varying the furance feed rate is also shown.

a. Treatment of a mixture of speiss and iron pyrites as the sulphur-containing reagent.

For a blowing rate of 3.8 Ft.3 Min.-' and furnace temperature 800"C a mixture containing 10.8% As, 15.0% S, was fed into the furance at 8.9 Kg Hr.-1. The resulting calcine contained 4.15% As, 5% S.

When the same mixture was fed into the furance at 13.7 Kg Hr.-' the resulting calcine contained 1.2% As, 11.2% S.

b. Treatment of a mixture of speiss and a tin concentrate as the sulphur containing reagent.

For a blowing rate of 4 Ft.3 Min.-' and a furance temperature of 800"C a mixture containing 7.5% As, 13.4% S was fed to the furance at 14.7 Kg Hr.-'. The resulting clacine contained 1.5% As, 3.7% S.

c. Treatment of a mixture of speiss and flowers of sulphur as the sulphur containing reagent.

For a blowing rate of 4 Ft.3 Min.-' and a furnace temperature of 800-810 C a mixture containing 15.9% As, 22.9% S was fed to the furnace at 9.23 Kg Her.~'. The resulting calcine contained 1.1% As, 5.5% S.

The tests set out above show the desirability of feeding an excess of sulphur over that stoichiometrically required to react with the oxygen-containing gas.

Also, alternative sulphur sources are illustrated in EXAMPLE 2 above.

1. A process for removing arsenic from a particulate arsenic-containing solid, comprising

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A method of removing arsenic from solid pyrometallurgical products This invention relates to a method of removing arsenic from pyrometallurgical products produced during the smelting of non-ferrous metals and more especially to the removal of arsenic from speisses. In the smelting of complex materials containing e.g. tin, lead, copper with arsenic and iron, a compound of iron and arsenic called 'speiss', holding minor amounts of other nonferrous metals, separates as a less-dense layer in the furnace-ladle or forehearth. It is common practice to augment the iron in the charge to capture as much arsenic as possible-though this also incurs the loss of valuable metals, for instance, tin and precious metals. The iron-arsenic phase can contain up to 30% arsenic in the most favourable cases. Many smelters have for long regarded this speiss as the most suitable material for longterm disposal of arsenic by dumping, but the valuable metal contents are sometimes too high for dumping, and there is now doubt about the long-term stability of speisses. It is an object of this invention to remove arsenic from such products as speisses in a highly-efficient manner, to leave a residue substantially free of arsenic, and to produce a concentrated arsenic-containing solid for disposal by encapsulation or dumping or suitable for working-up into valuable arsenic compounds. This invention consists in a process for removing arsenic from a particulate arsenic containing solid, comprising heating the solid either in the presence of a sulphur source in an oxygen-containing gas stream or in a stream of a sulphur dioxide-containing gas, and fuming off arsenic sulphide in the gas stream. Preferably the oxygen-containing or S02-containing gas is employed to fluidise the particles of arsenic-containing solid. Preferably the sulphur source is selected from pyrites, elemental sulphur and metal sulphide concentrates. Preferably the arsenic-containing solid is a speiss. Preferably the oxygen in the gas is insufficient to convert all the sulphur in the sulphursource to sulphur dioxide. Preferably the temperature within the reactor is within the range of 500"-900"C. The invention will now be further described and illustrated by reference to the following non-limiting Examples. EXAMPLE I Tests were conducted using a tube furnace operating at 800"C. a. In the first test a mixture of speiss and pyrite were heated together whilst a stream of air was passed through the tube. This produced a calcine containing 0.63% As and represented 93.85% removal of the arsenic. b. In the second test a similar mixture was heated in the same way but a stream of pure nitrogen was passed through the tube. The calcine produced in this case contained 10.01% As representing little or no removal of the arsenic. c. A third test was carried out using speiss alone and a stream of pure sulphur dioxide was passed through the tube. The calcine produced contained 0.21 % As, representing 98.22% removal of the arsenic. So from test 'a' we deduce that.volatile arsenic sulphide is produced either from intimate contact between the speiss and the iron pyrites or from sulphur dioxide produced as the pyrite is burnt in the air stream. Test 'b' eliminates the former and test 'c' substantiates the latter. EXAMPLE 2 Using a 6" diameter pilot scale fluid bed reactor the following results were obtained for certain mixtures of speiss and sulphur containing reagent. The effect of varying the furance feed rate is also shown. a. Treatment of a mixture of speiss and iron pyrites as the sulphur-containing reagent. For a blowing rate of 3.8 Ft.3 Min.-' and furnace temperature 800"C a mixture containing 10.8% As, 15.0% S, was fed into the furance at 8.9 Kg Hr.-1. The resulting calcine contained 4.15% As, 5% S. When the same mixture was fed into the furance at 13.7 Kg Hr.-' the resulting calcine contained 1.2% As, 11.2% S. b. Treatment of a mixture of speiss and a tin concentrate as the sulphur containing reagent. For a blowing rate of 4 Ft.3 Min.-' and a furance temperature of 800"C a mixture containing 7.5% As, 13.4% S was fed to the furance at 14.7 Kg Hr.-'. The resulting clacine contained 1.5% As, 3.7% S. c. Treatment of a mixture of speiss and flowers of sulphur as the sulphur containing reagent. For a blowing rate of 4 Ft.3 Min.-' and a furnace temperature of 800-810 C a mixture containing 15.9% As, 22.9% S was fed to the furnace at 9.23 Kg Her.~'. The resulting calcine contained 1.1% As, 5.5% S. The tests set out above show the desirability of feeding an excess of sulphur over that stoichiometrically required to react with the oxygen-containing gas. Also, alternative sulphur sources are illustrated in EXAMPLE 2 above. CLAIMS

1. A process for removing arsenic from a particulate arsenic-containing solid, comprising heating the solid either in the presence of a sulphur source in an oxygen-containing gas stream or in a stream of a sulphur dioxidecontaining gas, and fuming off arsenic sulphide in the gas stream.

2. A process as claimed in claim 1 where the oxygen-containing or sulphur dioxide-containing gas is used to fluidise the particulate solid.

3. A process as claimed in claim 1, wherein the sulphur-source is selected from pyrites, elemental sulphur and metal sulphide concentrates.

4. A process as claimed in any preceding claim wherein the solid is a speiss.

5. A process as claimed in any one preceding claim, wherein the oxygen in the oxygen-containing gas is insufficient to convert all the sulphur in the sulphur-source to sulphur dioxide.

6. A process for removing .arsenic from speiss, substantially as hereinbefore described.

6. A process for removing arsenic from speiss, substantially as hereinbefore described.

CLAIMS Amendments to the claims have been filed, and have the following effect: New or textually amended claims have been filed as follows:

1. A process for removing arsenic from a solid arsenic-containing product of a pyrometallurgical process, comprising heating the product either in the presence of a sulphur source in an oxygen-containing gas stream or in a stream of a sulphur dioxide-containing gas, and fuming off arsenic sulphide in the gas stream.

2. A process as claimed in claim 1 where the solid is particulate and the oxygen-containing or sulphur dioxide-containing gas is used to fluidise the particulate solid

4. A process as claimed in any preceding claim wherein the solid is a speiss.

5. A process as claimed in any one preceding claim, wherein the oxygen in the oxygen-containing gas is insufficient to convert all the sulphur in the sulphur-cource to sulphur dioxide.