CA1213257A

CA1213257A - Method of electrum beneficiation

Info

Publication number: CA1213257A
Application number: CA000451199A
Authority: CA
Inventors: Masayuki Hisatsune; Naofumi Shibukawa; Ryoichi Nakayama
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 1983-04-19
Filing date: 1984-04-03
Publication date: 1986-10-28
Also published as: JPS615778B2; AU558638B2; JPS59196767A; AU2641584A

Abstract

ABSTRACT OF THE DISCLOSURE

A method of electrum beneficiation is disclosed. The method comprises grinding electrum-containing ore to fine particles, passing them through a high-gradient magnetic separator which comprises an air-core magnetic field filled with a matrix element, and recovering the electrum as magnetics. The method achieves high electrum recovery percentage and high gold or silver content in the electrum concentrate.

Description

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, i ,, ,' METHOD OF ELECT RUM BENEFICIATION
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BACKGROUND OF THE INVENTION
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The present invention relates to an elect rum beneficiation method by magnetic separation.
Elect rum, a native alloy of gold and silver, is --I conventionally recovered by cyanidation, amalgamation, it; gravity concentration, flotation or a combination of these methods, but no attempt has been made to extract elect rum by magnetic separation. This is because with only few exceptions, gold and silver, whether they are in the elemental form or in compound form, have been regarded as being diamagnetic, and hence, it has been considered impossible to recover elect rum by magnetic separation However, as a result of various studies made to recover elect rum by magnetic separation, the present inventors have I unexpectedly found that elect rum in its ore is paramagnetic ¦ rather than diamagnetic.
SUMMARY OF THE INVENTION
I` The primary object of the present invention is to provide a beneficiation method that is capable of extracting I` an elect rum concentrate from its ore in an industrially feasible high recovery percentage by a simple method of magnetic separation.

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I' ~L3Z57 This object can be achieved by a process wherein elect rum containing ore is milled to fine particles, which are then passed through a high-gradient magnetic separator having an air-core magnetic field filled with a matrix element, thereby recovering the elect rum as magnetic DETAILED DESCRIPTION OF THE INVENTION
Elect rum in its ore is present in the form of fine particles, and therefore, in order to recover it by magnetic separation the ore must be pulverized into particles of a size of about 40 em or less. The pulverization may be performed by any known device such as a ball mill. Balls are preferably made of a non-magnetic material such as alumina since the dust from worn balls will not reduce the purity of magnetic obtained in the subsequent stage of magnetic separation. The fine particles of elect rum ore are mixed with water to form a pulp, to which a dispersant may optionally be added to provide a uniform dispersion of the particles. The pulp is then fed into a high-gradient magnetic separator which comprises an electromagnet and a I matrix element made of fine ferromagnetic wires The matrix element is placed in the air-core magnetic field of the electromagnet in such a manner that the lines of magnetic force are concentrated by that matrix element. For the purpose of the present invention, the strength of the magnetic field must be at least 9,000 Ox, below which the :, ~l2~3Z~;7 recovery percentage of elect rum is decreased. An air-core magnetic field having a strength exceeding 20,000 Ox does I, not provide any corresponding advantage, and instead, the fabrication of the magnetic separator becomes difficult or the power consumption is increased. Therefore, the air-core magnetic field used in the present invention preferably has l a strength in the range of 9,000 to 20,000 Ox. The matrix Jo element preferably consists of ferromagnetic wires of a I fineness of 300 em or below With thicker wires, the ; 10 recovery percentage of elect rum is reduced. The feed rate through the magnetic separator is preferably in the range of 10 to 50 m/hr. If the feed rate is lower than 10 mar materials other than elect rum are entrapped by the fibrous matrix element and reduce the purity of the recovered concentrate. A feed rate higher than 50 mar is also undesired because it reduces the recovery percentage of elect rum.
By passing the elect rum containing ore through the hiyh-gradient magnetic separator under the conditions specified above, the elect rum concentrate is recovered as magnetic whereas diamagnetic guying minerals and host rock are rejected as nonmagnetic. If desired, the magnetic may be passed through the magnetic separator several times in order to obtain a concentrate of higher purity and I middlings.

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2~3~i7 As will ye apparent from the foregoing description, the beneficiation method of the present invention achieves high concentrate ratio and recovery percentage in extracting elect rum from its ore by the previously inopera~vemagnetic separation The resulting concentrate of high purity can be further purified in copper smelting and other refining operations involving gold or silver recovery steps. The middlings may be refined by cyanidation, and this is another feature that adds to the commercial value of the ' lo present invention.
to The present invention is hereunder described in greater detail by reference to the following examples which to are given here for illustrative purposes only and are by no means intended to limit the scope of the invention.
1.5 Example 1 Electrum-containing siliceous ore (200 g) was commented into particles finer than 40 em with a rod mill and a ball mill using stainless steel balls. Water was added to the powder to melee a pulp (3,000 ml), which was mixed with sodium silicate (5 kg/t) as a dispersant. The pulp was passed through a high-gradient magnetic separator comprising an air-core magnetic field (14,000 Ox) filled with fine ferromagnetic wires ( <300 my at a feed rate of I; 20 m/hr. Magnetic separated from nonmagnetic were further passed through another high-gradient magnetic to :

~2~32S7 separator comprising an archer magnetic field (9,000 Ox) filled with fine ferromagnetic wires (< 300 my at a feed rate of 40 m/hr. By this second separation, tune magnetic were separated into an elect rum concentrate and middlings.
The results of this working example are shown in Table 1, from which one can see that the beneficiation method of the present invention was able to provide an elect rum concentrate of high purity in a significantly improved recovery percentage.
Table 1 Content Recovery Percentage Weight (g/t) (%) Percent A A A A
1) Ore 100.00 /4 197 100.00 100.00 2) Concentrate 39.60 172 436 91.69 87.43

3) Middlings25.48 16 70 5.~9 9,03

4) Nonmagnetic 34.92 6 20 aye 3.54 2) + 3) 65.08 111 293 97.1~ 96.46 I Example 2 Electrum-containing siliceous ore (400 g) was commented into fine particles (-10 em: 91%) with a rod mill and a ball mill using alumina balls. Water was added to ~2~3ZS7 I, the powder to make a pulp (5,000 ml), which was mixed with sodium silicate (5 kg/t) as a dispersant. The pulp was passed through a high-gradient magnetic separator comprising an air-core magnetic field (19,500 Ox) filled with fine , 5 ferromagnetic wires ( ~300 my at a feed rate of 20 m/hr.'or Magnetic separated from nonmagnetic were further passed through another high-gradient magnetic separator having the ' same specifications as those of the first separator at the same feed rate. By this second separation, the magnetic , 10 were separated into an elect rum concentrate and middlings.
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The results of this working example are shown in Table 2, from which the advantages of the present invention (i.e.
very high concentrate ratio and recovery percentage) are obvious.
Table 2 Content Recovery Percentage I' Weight (g/t) (%) Percent A A A A
1) Ore 100.00 70 198 100.00 100.00 i' 20 2) Concentrate 12.26 492 1166 86.61 72.12 3) Middlings16.09 37 210 8.55 17.04 4) Nonmagnetic 71.654.7 30 4.84 10.84 2) + 3) 28.35 ~34 623 95.16 89.16 .... .
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Claims

WHAT IS CLAIMED IS:

1. A method of beneficiation of electrum or a native alloy of silver and gold, which comprises grinding electrum-containing ore to fine particles, passing them through a high-gradient magnetic separator which comprises an air-core magnetic field filled with a matrix element, and recovering the electrum as magnetics.

2. A method according to Claim 1 wherein the electrum-containing ore is ground to particles of a size of 40 µm or less.

3. A method according to Claim 2. wherein the grinding is performed with a ball mill using alumina balls.

4. A method according to Claim 1 wherein the air-core magnetic field has a strength of 9,000 to 20,000 Oe.

5. A method according to Claim 1 wherein said matrix element is comprised of fine ferromagnetic wires.

6. A method according to Claim 5 wherein said fine ferromagnetic wires have a diameter of 300 µm or less.

7. A method acording to Claim 1 wherein the ground particles of electrum-containing ore are passed through the magnetic separator at a feed rate of 10 to 50 m/hr.