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5 Methods of Gold-Silver Ore Extraction

Xinhai 2020-10-16(02:10:11) 289 0

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Gold-silver ore is a kind of ore that is relatively difficult to extract. In addition to gold, each ton of ore contains dozens to hundreds of grams of silver. So, how can we separate silver and gold? We will give a specific introduction below.

1. State of Silver in Gold-Silver Ore

In the primary gold-silver ore, silver is often present in the form of sulphur-antimony copper silver ore, brittle silver ore, spiral sulphur silver ore, crimson silver ore, light red silver ore and natural silver. Silver tellurides (tellurium silver mine, tellurium gold and silver mine, needle tellurium gold mine) can also be seen in it, but relatively few.

In the oxidized ore, there are silver halides-mainly chlorargyrite, sulfate (argentojarosite) and natural silver.

In these ores, silver minerals often coexist closely with clay minerals, manganese oxide and iron oxide. Natural silver particles are often covered by thin films formed by some metal hydroxides and oxides.

Some sulfides (pyrite, chalcopyrite, galena and antimonite) are also enriched with silver particles. The silver content of galena is as high as 0.1%, sometimes 0.5-1%. The grinding process can not dissociate such fine silver particles.

2. Extraction Method of Silver in Gold-Silver Ore

#1 Gravity Separation Method

Silver can be enriched by gravity separation, but its enrichment degree is much lower than that of gold. It is usually processed by a jig to collect coarse (greater than 0.1~0.2 mm) heavy minerals, namely natural silver, argyrite and hornsilite.

These minerals have respectively high specific gravity (10.1~11.1; 7.2 and 5.5), and also have ductility, which can prevent them from being over crushed. The remaining silver minerals are very brittle and become very fine during the grinding process, making it difficult to recover using a jig.

It can be seen that in order to improve the gold recovery rate during the gravity separation method, stage grinding must be adopted to reduce the over-grinding of silver minerals, and other more effective methods should be used to replace jig operations.

Gravity sparation Machine-Jig (1).jpg

#2 Amalgamation Method

In fact, only natural silver can be recovered from all silver minerals by the amalgamation method. However, it should be pointed out that compared with gold, silver itself is not easily wetted by mercury, and the surface of silver particles is often covered with various films that hinder the amalgamation process than gold particles. Therefore, the amalgamation method only makes practical sense when deal with the treatment of gravity concentrates.

#3 Cyanidation Method

Many gold-silver ores, especially oxidized ores can be processed by cyanidation method. In the process of cyanidation, chlorargyrite dissolves fastest, but natural silver and the simple sulfides of silver that form natural alloys of natural silver and other metals (argentite, spiral pyrite) are more difficult to dissolve. The sulphur antimony copper silver ore and argentojarosite cannot be extracted by cyanidation.

When formulating a cyanidation system for silver-containing ore, the following measures should be taken:

1) Leach with concentrated cyanide solution (0.2~0.6% NaCN);

2) Long time (up to 2 to 3 days) leaching;

3) Inflate strongly into the pulp;

4) Add lead salt to the pulp;

5) Bromine cyanidation and so on.

During the cyanidation of ores containing silver arsenide or telluride, it is beneficial to add oxidants such as manganese dioxide, potassium permanganate, sodium peroxide or barium peroxide.

#4 Flotation Method

Most silver minerals use sulfhydryl collectors during flotation. Natural silver with clean surface and silver sulfide and telluride (argentite, light red silver ore, sulphur antimony copper silver ore, brittle silver ore) are very easy to float.

Lime has an inhibitory effect on the floatation of sulphur-copper-silver ore, light red silver ore and deep red silver ore. However, it has less influence on tellurium silver ore and argentite. Cyanide and sodium sulfide have a strong inhibitory effect on many silver minerals, especially natural silver.

There are many types of silver minerals, and it is difficult to achieve the purpose of discarding tailings by flotation alone. The use of sulfhydryl collectors in combination with hydroxyl collectors, stage flotation, and desliming can improve the recovery rate of silver minerals in flotation concentrates.

Flotation Cell (1).jpg

#5 Roasting-Cyanidation Method

For many flotation concentrates and gravity concentrates containing silver, roasting must be performed before cyanidation. Oxidation roasting can decompose telluride, selenide, and simple sulfides and complex sulfides of silver, and can expose silver that is wrapped in pyrite, chalcopyrite and other sulfides (except galena).

During the oxidation roasting process, galena will decompose into fusible oxides and sulfates, and when it cools, it will solidify into very strong particles with the silver wrapped in it. Therefore, silver is not exposed, so that it cannot be recovered using cyanidation.

The cyanidation effect of calcine depends to a large extent on the temperature system of oxidation roasting. The best roasting temperature is usually 600°C. Higher or lower temperature will reduce the recovery rate of silver during cyanidation. Silver-containing iron sulfide is better to be roasted in two stages: the first stage has a roasting temperature of 450~ 550℃ and the second stage 550~650℃.

If the roasting can produce coarse silver beads or silver matte, it should be recovered by gravity separation before cyanidation.

Products containing deep red silver ore, light red silver ore, other complex sulfides of silver and argentojarosite can be processed by chlorination roasting. The silver chloride obtained by roasting is easily dissolved in the cyanidation process. But the chlorination roasting has the following disadvantages:

1) The consumption of sodium chloride is large (up to 10~15% of the weight of the material);

2) The chlorides of gold and silver will volatilize and escape, causing the loss of gold and silver. Materials containing silver and copper are best to use chlorinated-reductive roasting (segregation method). In this kind of roasting, copper chloride and silver chloride are first generated, and then reduced to metal and alloy particles. These particulate metals can be recovered from calcine by flotation or hydrometallurgy.

The main silver recovery methods and the relationship between their characteristics are listed in the table below.

The Characteristics of Silver in Ore and its Recovery Method
Characteristics of   Silver Recovery Method
Coarse   (greater than 0.1-0.2 mm) natural silver and natural alloysGravity Separation
Natural   silver and natural alloys in the form of free and continuous particles (less   than 0.1-0.2 mm)Cyanidation
Flotation and the next step   of cyaniding or smelting the concentrate
Free or   conjoined chlorargyrite particlesCyanidation*
Free   or conjoined form simple sulfide of silverFlotation and the next step of cyaniding or smelting the   concentrate
Free   or conjoined silver telluride, selenide, complex sulfide and silver iron   vanadium particlesOxidation roasting or chlorination roasting and cyanidation of   calcine
Flotation and the next step   of smelting or roasting the concentrate gold ore, and the calcine is treated   by cyanidation
Silver wrapped in galena,   chalcopyrite, chalcocite and other non-ferrous metal sulfidesFlotation and the next step of ore concentrate or smelting*
Silver wrapped in iron   sulfideFlotation and the next step of oxidative roasting or   chlorination roasting of the concentrate and cyanidation of the calcine*

*The coarse part of minerals can be recovered by gravity separation

The characteristics of silver listed in the table are the technological properties of silver mineral particles in the ore after grinding, that is, the properties that have the greatest impact on the metal recovery process.

However, silver in gold-silver ore is often not only in one state, but in multiple states, so a combined process composed of two or more methods is often used. In order to recover coarse-grained useful minerals, we should use a gravity separation method.

3. To Sum Up

In actual production, we should choose the process flow suitable for our mine according to the actual situation of the mine and with the help of the technicians to achieve the highest extraction efficiency.

If you have gold and silver ores that need to be extracted, please contact online customer service for consultation to obtain more detailed information and targeted process selection.

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