Method and apparatus for extracting high-purity gold from ore

Abstract

A method and plant for gold recovery from any gold-bearing ore by low-temperature chlorination, wherein the finely-divided gold-bearing feedstock is chlorinated gaseous chlorine at a temperature of about 245 C. to form a highly volatile chloride compound, which after leaving a reactor is directed to a low-temperature nitrogen plasma unit having a temperature of 900-1100 C., wherein the said compound decomposes and turns into high-purity gold powder, which is cooled with gaseous nitrogen at a cooling reactor's inlet, which is equipped with a water chamber, and collected in a dumping hopper. Some embodiments allow recovery of high-purity 999.9 fine gold using an environmentally friendly, cost effective and inexpensive method implemented on an industrial scale.

Claims

1. A method of extracting gold from gold-bearing material, comprising: chlorination of the gold-bearing material using gaseous chlorine at a temperature not greater than 245 C. to form a volatile chloride compound in a reactor; and decomposing the volatile chloride compound in a low-temperature nitrogen plasma unit having a temperature between 900 C. and 1100 C. to produce high-purity gold powder.

2. The method of claim 1, wherein the particle size of the gold-bearing material is 30-50 m.

3. The method of claim 1, wherein the reactor is blown down with an inert gas to remove air prior to the chlorination.

4. The method of claim 1, wherein the gold-bearing material is fed into the reactor through a screw in countercurrent to gaseous chlorine.

5. The method of claim 1, further comprising filtering the volatile chloride compound through a granular material to remove impurities before the decomposing in the plasma unit.

6. The method of claim 1, further comprising trapping particles of the gold powder in filtration sleeves.

7. The method of claim 1, wherein the reactor is not the plasma unit.

8. A method of extracting gold from gold-bearing material, comprising: chlorination of the gold-bearing material using gaseous chlorine at a temperature not greater than 245 C. to form a volatile chloride compound in a reactor; and decomposing the volatile chloride compound in a low-temperature nitrogen plasma unit having a temperature between 900 C. and 1100 C. to produce high-purity gold powder and further comprising: removing nitrogen from chlorine exiting the plasma unit; and transferring the chlorine to the reactor for reuse, or further comprising: generating chlorine leaks; and neutralizing the chlorine leaks with alkali in a scrubber.

9. An apparatus for the method of claim 1, comprising: a reactor for low-temperature chlorination of gold-bearing material capable of maintaining a temperature not greater than 245 C.; a low-temperature nitrogen plasma unit capable of operating at a temperature between 900 C. and 1100 C. for decomposition of volatile chlorinated gold compound generated in the reactor; and a source of nitrogen connected to the low-temperature nitrogen plasma unit.

10. The apparatus of claim 9, further comprising a filtration system between the reactor and the plasma unit for removal of impurities from the chlorinated gold compound.

11. The apparatus of claim 9, further comprising a hopper to collect the gold powder produced in the plasma unit.

12. The apparatus of claim 9, wherein the volatile chloride compound is Au.sub.2Cl.sub.6.

13. The apparatus of claim 9, wherein the reactor is not the plasma unit.

14. An apparatus for the method of claim 1, comprising: a reactor for low-temperature chlorination of gold-bearing material capable of maintaining a temperature not greater than 245 C.; a low-temperature nitrogen plasma unit capable of operating at a temperature between 900 C. and 1100 C. for decomposition of volatile chlorinated gold compound generated in the reactor; and a filtration system between the reactor and the plasma unit for removal of impurities from the chlorinated gold compound, wherein the filtration system comprises at least one filter comprising granular reagents installed in a gas duct and designed specifically for trapping each impurity.

15. An apparatus for the method of claim 1, comprising: a reactor for low-temperature chlorination of gold-bearing material capable of maintaining a temperature not greater than 245 C.; a low-temperature nitrogen plasma unit capable of operating at a temperature between 900 C. and 1100 C. for decomposition of chlorinated gold compound generated in the reactor; a chlorine regenerator for separating gaseous chlorine from gaseous impurities for subsequent use in the chlorination reactor; and a scrubber connected to the chlorine regenerator for alkaline neutralization of chlorine leaks.

16. An apparatus for the method of claim 1, comprising: a reactor for low-temperature chlorination of gold-bearing material capable of maintaining a temperature not greater than 245 C.; a low-temperature nitrogen plasma unit capable of operating at a temperature between 900 C. and 1100 C. for decomposition of volatile chlorinated gold compound generated in the reactor; and a heater for heating gaseous chlorine up to between 50 C. and 70 C. before the gaseous chlorine enters the reactor.

17. An apparatus for the method of claim 1, comprising: a reactor for low-temperature chlorination of gold-bearing material capable of maintaining a temperature not greater than 245 C.; a low-temperature nitrogen plasma unit capable of operating at a temperature between 900 C. and 1100 C. for decomposition of chlorinated gold compound generated in the reactor; a chlorine regenerator for separating gaseous chlorine from gaseous impurities for subsequent use in the chlorination reactor; and a source of nitrogen connected to the low-temperature nitrogen plasma unit.

18. The method of claim 1, wherein the volatile chloride compound is Au.sub.2Cl.sub.6.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The drawing is not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. The FIGURE presents the workflow of the plant, which is one embodiment of the invention.

DETAILED DESCRIPTION

(2) One plant embodiment schematically illustrated in the FIGURE operates based on the low-temperature chlorination technology (LTC) and designed for the recovery of high-purity aurous chloride dimers (Au.sub.2Cl.sub.6) from any gold-bearing ores, which form a basis for the recovery of high-purity gold powders, while the plant's capacity makes up 6.0 tons per annum under single-shift work conditions.

(3) The whole process runs in a gas environment at a temperature of approximately 245 C. in a closed cycle with no harmful emissions into the atmosphere as all used chlorine is recycled, therefore the whole process is completely environmentally friendly.

(4) The plant comprises the following assemblies.

(5) The continuously operating LTC reactor, which handles chlorination of gold-bearing ore by gaseous chlorine.

(6) A specific nature of chlorination reactions at low temperatures in comparison with standard reactions (over 1000 C.) poses certain requirements to the design of the reactor and its operational mode.

(7) The reactor 1 is a cylindrical horizontally mounted chamber made of fused silica, resistant to such aggressive medium as chlorine at operational temperatures.

(8) The feedstock is supplied continuously by portions through a feed-control device, which automatically supplies a set amount of the feedstock to the reactor from a loading hopper, depending on the desired output.

(9) A carbon fiber plastic screw rotates in the reactor and mixes the supplied gold-bearing ore to evenly heat powders, pass gaseous chlorine and avoid agglomeration of powders.

(10) The system is preliminary blown down by argon or nitrogen at a rate of 100 l/min for air removal from the system, and all plant assemblies are simultaneously heated up to 245 C.

(11) The heating is provided by panel folding heaters equipped with embedded heating elements made of heat-resistant materials.

(12) Design of the panel folding heaters allows replacing heating elements without a need to dismantle the reactor's housing.

(13) Gaseous chlorine is supplied to the reactor 1 from a liquid chlorine bulb after passing through a heater 11 with a capacity of 501, where chlorine is heated to the temperature required for chlorination (approximately 60 C.).

(14) Gaseous chlorine is supplied in excess, approximately 4-5 times higher than stoichiometry, at a rate of 40 l/min for the most complete chlorination process.

(15) The chlorination process is carried out between gaseous reagents and solid raw materials; therefore, its effectiveness depends on the contact area between these phases, i.e. on the fineness degree of the raw material.

(16) The feedstock must be finely divided with a particle size of 30-50 m to ensure effectiveness of the process. The fine-dispersed raw material is fed into the reactor in countercurrent to chlorine.

(17) As a result, chlorination of gold-bearing ore takes place in the reactor 1. A temperature not exceeding 245 C. is required for the reaction. In this case the reaction changes gold only to Au.sub.2Cl.sub.6:
2Au(solid)+3Cl.sub.2(gas)=Au.sub.2Cl.sub.6(gas)

(18) This is an exothermic reaction, taking place with minor heat release.

(19) Given the specified temperatures, Au.sub.2Cl.sub.6 vapors having a sublimation temperature of 245 C. are mainly sublimated.

(20) It should be pointed out that some other elements, such as iron, vanadium, etc. presented in the gold-bearing ore are also sublimated along with aurous chloride vapors.

(21) Such components of gold-bearing ore, as silver, nonferrous metals, silicon, etc. do not react at process temperatures and remain in the charge.

(22) The chlorination process is characterized by the following parameters:

(23) operating flow rate of feedstock, in gold equivalent3.0 kg/h;

(24) feedstock fineness: 30-50 m;

(25) aurous chloride dimer recovery rate (Au.sub.2Cl.sub.6)4.65 kg/h;

(26) product fineness: 1-15 m; and

(27) system pressure: 15-20 mm Hg.

(28) Further, the obtained chlorination product (Au.sub.2Cl.sub.6) is sublimated and enters the gas duct 2 made of fused silica, where the gas mixture is purified from contaminating impurities with the sublimate going through filters 11 11 filled with granules of the corresponding reagents.

(29) Every filter 11 11 is a fused silica cylinder having one side open and a mesh bottom on the other side. The preferred configuration of the system has 3 filters sequentially arranged in the gas duct vertically one above the other.

(30) Granulated salt (NaCl) is used to purify the gas mixture from iron impurities and other components. NaCl turns into a non-volatile compound and settles on salt granules when reacting with iron chloride vapors.

(31) Fine copper chips are used to purify the mixture from vanadium impurities. When reacting with the chips, vanadium chloride vapors also turn into a non-volatile compound and settle on the copper chips.

(32) A granular zeolite (for example, erionite) is used for final purification of impurities, which purifies gaseous aurous chloride dimer from mechanical impurities and moisture.

(33) Reagents in the filters should be replaced in the course of production, depending on the amount of impurities contained in the feedstock. On average, the replacement takes place once every 7 days of plant operation.

(34) After passing through the filtration system 12, the gaseous Au.sub.2Cl.sub.6 purified of all impurities flows through the gas duct 2 to the low-temperature arc plasma unit 3, where Au.sub.2Cl.sub.6 decomposes in the low-temperature nitrogen plasma (900-1100 C.) and turns into high-purity gold powder.

(35) The type of the powder depends on the temperature, mode and residence time the gas flow in the plasma unit.

(36) The decomposition process using the low-temperature plasma is characterized by the following parameters: high-purity gold powder recovery rate: 3.0 kg/h; fineness of gold powder: 1-10 m (depending on the task, the fineness is regulated in the low-temperature plasma unit by adjusting the residence time of particles in the cooling reactor and the plasma temperature); and

(37) system pressure: 1 atm or 760 mm Hg.

(38) The obtained high-purity gold powders are cooled in the reactor 4, which is cooled by cold running water circulating through a cooling circuit.

(39) Then, the powder settles in the receiving hopper 5, while smaller unsettled particles are removed with the gas stream and trapped in the filtration sleeves 6 made of heat-resistant material and the cyclone filters 7.

(40) Fineness of the gold powder is regulated by the residence time in the cooling reactor, which is usually a hundredth of a second.

(41) The main high-purity gold powder settles under the action of a centrifugal force initiated by a stream of purified air.

(42) The waste gas mixture containing chlorine derived from the decomposition of aurous chloride dimer, as well as nitrogen, enters the chlorine regeneration assembly 8, where gaseous chlorine is separated from nitrogen and reused in the reactor 1.

(43) For safety purposes, the fiberglass scrubber 9 containing a solution of NaOH to neutralize chlorine is also provided at the outlet to catch chlorine, which may be released in emergencies or as a result of a breakthrough.

(44) The plant enables recovery of high-purity aurous chloride dimers of 999.9 fine that are further used to produce high-purity 999.9 fine gold powders by means of the low-temperature plasma.

(45) The proposed method makes it possible to use core process equipment (chlorination reactor, sublimation filters, gas ducts, finished product condensers) made of fused silica or heat-resistant glass to realize the process.

(46) Power consumption of the complete set of equipment makes up a maximum of 125 kW/h.

(47) The complete set of equipment requires the area of about 10 m.sup.2 and the production shop100 m.sup.2 at most given a ceiling height of 3.5 m.

(48) Moreover, the plant does not require to be connected to the acid drainage system and does not emit harmful substances into the atmosphere as it operates based on a fully closed cycle.

(49) A set of equipment arranged in one embodiment enables production of high-purity 999.9 fine gold powders with a capacity of 6.0 tons per annum given an 8-hour working day, which is an unprecedented result having no analogues in the world.

(50) While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.