AU2004200698A1 - Process for Treating Gold Ores with Stibnite - Google Patents

Description

TITLE OF THE INVENTION Process for treating gold ores with stibnite FIELD OF THE INVENTION This invention relates to a process for treating gold ores with stibnite. More particularly, the ore or its concentrate is firstly treated with the solution of a water-soluble alkaline sulphide to form a solution containing antimony compound, while gold and gangue are left as solid relicts.

The antimony containing solution is then treated with a double-layered oxide which absorbs the antimony compound. This double-layered oxide can be re-activated by heating and is re-usable several times until it is fully loaded with antimony compound. This fully loaded double-layered oxide can then be sent to process and recover the antimony. Gold in the relict solid can be extracted with conventional extraction methods.

BACKGROUND OF THE INVENTION Stibnite (Sb 2

S

3 is the main source of antimony metal and usually occurs in quartz veins with or without lead-zinc (Pb-Zn) sulphides. In nature, it is very common to find gold and antimony in the same ore body. This type of ore usually contains 1 10 g/T of gold and 1 18 of antinomy. Gold is usually in the form of fine native gold particles and the antimony is in the form of stibnite in this type of assemblage.

Once the quantity of stibnite in the ore is sufficiently high, then stibnite has a detrimental effect on the commonly used cyanide gold leaching process. Under the conditions applied for gold leaching, stibnite consumes cyanide before the gold does and thus acts as a cyanicide.

The reaction can be seen in the following equations: Sb 2

S

3 6NaOH Na 3 SbO 3 Na 3 SbS 3

H

2 0 2Na 3 SbS 3 3NaCN 1.50 2 3H 2 0 Sb2S 3 +3NaCNS 6NaOH That is, during the cyanide leaching process, firstly stibnite reacts with caustic soda (NaOH) and forms water-soluble sodium antimonite (Na 3 SbO 3 and sodium sulphantimonite (Na 3 SbS 3 The latter will then react with cyanide in the solution and forms an insoluble antimony sulphide (Sb 2

S

3 This Sb 2

S

3 will deposit on the surface of gold particles to form a protective film and thus hinders the dissolution of gold in cyanide solution. Therefore, it is generally regarded that the cyanide leaching method is not suitable for gold ores with stibnite.

Traditional methods of processing gold ores with stibnite are as follows. Ores were initially pulverized and sulphides were concentrated by flotation methods. The gold flotation concentrates were calcined at carefully controlled temperatures. Antimony was collected in the flue as antimony oxide (Sb20 3 The majority of gold remained in the calcined matte which can be extracted by the conventional methods such as cyanide leaching etc. However, a serious drawback of this method is that a considerable amount of gold can be carried by the antimony into the flue or even escape into the atmosphere, both of these reduce the total recovery of gold.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention can be used to process the unprocessed gold ores with stibnite and also the gold containing stibnite concentrates after mineral dressings. Gold is mainly in the form of native gold fine particles and the antimony is in the form of stibnite in the original ores or concentrates. The original ores should be ground to <100 mesh, whereas no grinding will be required for the concentrate.

The ore or concentrate should be treated in a cylindrical slurry tank with a depth of 1 to 2 times of its diameter. A mechanical stirrer is located in the middle of the tank to ensure the homogeneous mixing of ore or concentrate with the sulphide solution. Sulphides can be either one of the following: e.g. lithium sulphide (Li 2 sodium sulphide (Na 2 potassium sulphide (K 2 S) and ammonium sulphide ((NH 4 2 or the mixture of several of them. For the cost concerns, Na 2 S is recommended. The stibnite will react with the S 2 ions in the solution and become soluble antimonite: Sb 2

S

3 +3S- 2 2SbS Excess sulphides should be added to ensure that stibnite be totally dissolved. If the sulphide used is Na 2 S, the amount of sulphide required is approximately the same as that of stibnite (in weight). If not enough sulphide is added, then the dissolution of stibnite will be incomplete.

However, when too much of excess amount of sulphide is added, it will not only increase the production cost, but will also reduce the antimonite absorption rate in the next stage of the process.

After stibnite has dissolved, gold is left in the solid phase and it can be leached out using the traditional cyanide-leaching process.

The typical chemical reaction for the layered double oxide (hereafter called LDO) for absorbing antimonite in this invention can be expressed as: 3Mg 6 Sb 2 0 9 35H20 2SbS< 2[MggSb(OH) 8 3 (SbS 3 4H 2 0 The amount of antimonite absorbed by the LDO is restricted by the above chemical reaction.

Considering the interferences from S 2 OH- and CO 2 left in the solution, excessive amount of LDO should be added. The actual amount of LDO required should be about 10 20 times of the antimony in the solution (in weight). After the absorption process, a small amount of SbS33- and S 2 ions will still be left in the solution. Therefore, the solution should be re-cycled and pumped back to the slurry tank.

The LDO is a synthesized material containing two different oxidation states of metal oxides.

It has a layered type structure similar to that found in the natural mineral of brucite, which is a derivative form of the mineral hydrotalcite. These types of minerals are sometimes called the anion-clays. The chemical formula for hydrotalcite is [MlIxMxII(OH) 2 where M" is divalent metal cations e.g. Mg 2 Zn 2 Fe 2 Mn 2 Co 2 Ni 2 Cu 2 and Ca 2 etc; is trivalent metal cations e.g. A13+, Sb 3 Fe 3 Cr 3 Co 3 and Mn 3 etc; can be anions e.g. CO32-, N03- and S042- etc; with x 0.5 0.17 and 1 The above structure can be regarded as some of the divalent cations in the crystal structure of brucite having been partly replaced by the trivalent cations. In order to balance the charges in the structure, anions and water molecules have to be filled in the space between the layers.

The hydrotalcite will lose these in-filled anions and water molecules after being calcined at 450 to 750 C and the final product will be a LDO. The general formula for the LDO is M"mM"',Ox, whereas x m 3n/2. A typical reaction of the heating can be expressed as: 3[MgSb(OH), 2 CO -4H 2 0 7.50 2 3MgSb20 9 +3CO 2 36H 2 0 The LDO can recover its hydrotalcite structure after absorbing anions and water from the surroundings. Because it has a high specific area and large pore sizes, it can easily absorb foreign materials. Therefore, it can be used to absorb the antimonite radicals in the solution.

The LDO used in this invention is oxides of magnesium and antimony, the divalent oxide is MgO and the trivalent oxide is Sb 2 03 with molecular ratio between 1 to 5 1.

The magnesium-antimony double-oxides system is a derivative of hydrotalcite. It is synthesized by the wet-grinding and hydrolysis methods in this invention. Details of the synthesis are as follows.

1. Measure MgO or Mg(OH) 2 and Sb 2 03 according to the molar ratio of 2:1 to 5:1. Charge the mixture into a ball mill or rod mill with 2 8 times of water and mill for 6 24 hours.

2. Measure soluble carbonate or bicarbonate, which is 0.2 1.5 times of the weight of Sb203, and add it into the above mixture. At temperatures between the room temperature and 90°C, continuously stir for 10 48 hours to ensure the completion of hydrolysis process. Remove water from the hydrolysate by filtration, sedimentation or centrifuge, and wash it with clean water for 2 3 times, then dry it at temperatures below Bake the hydrolysate at a temperatures between 500°C and 750 C for 2 5 hours, then grind to <200 mesh. The final product is a material with a general formula of: [Mgl-xSbx(OH) 2

]X+[(HCO

3 )x.nH20], or [Mgl-xSbx(OH) 2

]X+[(CO

3 2 .nH2 0 where X 0.5 0.17, n 2 8 and Mg/Sb 2 Compared to the traditional method of co-precipitation for producing hydrotalcites, the method mentioned in this invention is simpler, raw materials are cheaper and there is no discharging of waste water.

As a result of the absorption of antimonite radicals, the colour of LDO becomes bluish grey.

After drying, it will be calcined in an oven at a temperature between 5000 to 750°C. The oven should have sealed walls and a long flue to facilitate the recovery of volatiles. Typical reaction during the roasting is: [Mg 3 Sb(OH), 3 (SbS 3 4H 20 602 3Mg 3 Sb, 33 0 5 +3SO 3 +16H 2 0 The antimonite radicals absorbed by the LDO are disintegrated and turned into antimony oxide which is locked in the molecular structure of LDO. The SO 3 in the flue gas can be recovered for the production of sulphuric acid as indicated in the following equation: SO, H20 HSO 4 The calcined product is still LDO and can be re-used several times.

After being re-cycled 3 10 times, because the amount of Sb 2 03 in the LDO has been increased, its ability of absorbing antimonite radicals decreased. It is then the time to recover the antimony. This antimony-loaded LDO can be sold to antimony smelters or be processed locally. That is to roast the LDO between 1000°C and 1500°C for 2 6 hours. The Sb20 3 will be sublimed from the LDO and collected in the flue. Residue of the roast is magnesium oxide (MgO).

Alternatively, after being re-cycled 3 10 times, the LDO can be re-activated through the wet-grinding and hydrolysis processes by: 1. Add magnesium oxide (MgO) or magnesium hydroxide (Mg (OH)2) into the spent LDO at weight ratios of 0.1:1 to 3:1 respectively. Place the mixture into a ball mill or a rod mill with additional 2 8 times of water, then mill for 6 12 hours.

2. Measure soluble carbonate or bicarbonate, which is 0.2 1.5 times of the weight of Sb 2 03, and add it into the above mixture. Continuously stir for 10 48 hours to ensure the completion of hydrolysis process. Remove water from the hydrolysate by filtration, sedimentation or centrifuge, and wash it with clean water for 2 3 times, then dry it at temperatures below 90 0 C. Bake the hydrolysate at a temperatures between 500 0 C and 750°C for 2 5 hours, then grind to <200 mesh.

Because magnesium oxide (MgO), magnesium hydroxide (Mg(OH) 2 and antimony oxide (Sb 2 03) are all slightly soluble in water, the wet-grinding can achieve the homogenous mixing down to the molecular scales. The mixture is hydrolyzed in the carbonate/bicarbonate solution and forms hydrotalcite. The typical chemical reaction in the solution can be seen in the following equations.

2Mg 3 SbO 4 5 17H 2 0 2HCO 3 2[Mg 3 Sb(OH) 8

](HCO

3 )4H 2 0 2(OH) 2Mg 3 SbO4.5 17H 2 0 CO, [Mg 3 Sb(OH) 8 ]2 (CO 3 8H 2 0 2(OH) In practice, an excess amount of carbonate/bicarbonate should be added to ensure the completion of the reaction. The type of carbonate/bicarbonate has little effect on the results of hydrolysis produced. For the consideration of costs, sodium carbonate/bicarbonate is preferable. The hydrolysate should be washed 2 3 times after removal of water to remove the excessive amount of bicarbonate.

EXAMPLES

Examples of the process of this invention in the laboratory are described as follows: EXAMPLE 1: Separating antimony from Gold Ore with Stibnite 1. The ore contained 3 g/T of gold and 5 of antimony. The ore was milled to <100 mesh.

Placed 100 g of the ore powder in the slurry tank together with 5 g of Na 2 S and 300 g of water. Continuously stirred for 1 hour, so the stibnite was totally dissolved.

2. Filtered the slurry and washed the solid phase twice with water. Combined the washing water with the filtrate. The solid phase was retained for gold leaching process.

3. Added 80 g of LDO into the liquid phase and continuously stirred for 10 hours.

4. Filtered the suspension. Liquid phase was re-cycled to Step 2 and solid phase was dried at 80 0

C.

The solid phase was calcined at 650 0 C for 3 hours. SO 3 in the flue was collected in a "Sulphuric Acid Generator" and the calcined solid was re-cycled to Step 3.

EXAMPLE 2: Separating Antimony from Concentrate containing Gold and Stibnite 1. The concentrate contained 20 g/T of gold and 30% of antimony. Placed 100 g of the concentrate in the slurry tank together with 40 g of Na 2 S and 800 g of water.

Continuously stirred for 2 hour, so the stibnite was totally dissolved.

2. Filtered the slurry and washed the solid phase twice with water. Combined the washing water with the liquid phase. The solid phase was retained for gold leaching process.

3. Added 400 g of LDO into the liquid phase and continuously stirred for 10 hours.

4. Filtered the mixture. Liquid phase was re-cycled to Step 2 and solid phase was dried at 0

C.

The solid phase was calcined at 650 0 C for 3 hours. SO 3 in the flue was collected in a "Sulphuric Acid Generator" and the calcined solid was re-cycled to Step 3.

EXAMPLE 3: Preparation of Hydrotalcite using Wet-grinding and Hydrolysis Processes 1. Placed 80 g of MgO and 292 g of Sb20 3 into the ball mill with 372 g of water and ground for 6 hours.

2. Added 88 g of NaHCO 3 into the mixture and continuously stirred at 60 0 C for 10 hours.

Filtered the mixture, then washed the solid phase twice with water.

3. Dried the solid phase at 80C and ground to <200 mesh.

EXAMPLE 4: Preparation of Hydrotalcite using Wet-grinding and Hydrolysis Processes 1. Placed 290 g of Mg(OH) 2 and 292 g of Sb 2 0 3 into the ball mill with 3000 g of water and ground for 24 hours.

2. Added 80 g of Na 2

CO

3 into the mixture and continuously stirred at 60 0 C for 10 hours.

Filtered the mixture, then washed the solid phase twice with water.

3. Dried the solid phase at 80C and ground to <200 mesh.

EXAMPLE 5: Preparation of LDO 1. Hydrotalcites prepared from Examples 3 and 4 were placed into a muffler furnace. They were calcined at 550 0 C for 3 hours.

EXAMPLE 6: Recovery of Antimony from the spent LDO 1. The LDO which had been re-cycled 10 times in Example 3 was collected. It was calcined in an oven at 1200 0 C for 3 hours. The Sb 2 0 3 powder was condensed on the inner walls of the flue and collected. The calcined residue was MgO and re-cycled in Example 3.

EXAMPLE 7: Re-activate the spent LDO 1. The LDO which had been re-cycled 8 times in Example 3 was collected. It was mixed with MgO according to the weight ratio of 0.2:1. The mixture was charged into a ball mill with 3 times of water and milled for 8 hours.

2. The NaHCO 3 which was 0.3 times the weight of LDO was added into the above mixture.

They were continuously stirred at 60 0 C for 24 hours to achieve the hydrolysis process.

The hydrolysate was filtered and washed twice, then dried at 70 0 C. It was calcined at 550 0 C for 3 hours and finally ground to <200 mesh.