Study on Pre-oxidation and Cyanide Gold Extraction of a Gold Ore Leaching Flotation Concentrate
In China, many mine tailings stockpiles are stored or continue to emit cyanide tailings of gold ore, and sulfides in raw ore are wrapped in gold to make certain tailings have higher gold grades. Such tailings are firstly enriched by gold by flotation process, and gold concentrate can be obtained at a very low mining and grinding cost, and the concentrate can be pretreated to effectively recover the gold. In this paper, a gold ore cyanide tailings flotation concentrate is treated by normal temperature and atmospheric pressure enhanced alkali leaching pre-oxidation process [1-3] .
First, the test
(1) Test materials
Test material is a flotation concentrate, gold grade gold ore tailings cyanide was 29.78g / t, silver-containing 15.07g / t, arsenic containing 0.64%, sulfur 19.90%, iron-containing 18.20%, SiO 2 45.74 %, Al 2 O 3 8.78%. The gold in the material is microscopic invisible gold and is mainly wrapped in pyrite. It is treated by ultra-fine grinding-cyanide method, and cyanidation is carried out for 24 hours under the grinding fineness of 99.5% of 99 μm. The leaching rate of gold is only 3.95%, which is difficult to leach. The reagents used are mainly: NaOH (IR), NaCN (AR), CaO (IR), activated carbon (IR).
(2) Test procedures and equipment
Process: Cyanide tailings flotation refractory gold concentrate is superfinely ground through a tower type grinding machine, and then enters a strengthened alkali immersion stirred tank for alkaline normal temperature and atmospheric pressure strengthening pre-oxidation, pre-oxidized pulp plus CaO milk slurry And filtering, the filtrate is returned to the alkali leaching pre-oxidation, and the filter residue is added to the new water slurry to enter the cyanidation and carbon adsorption operation. The instruments used in the test mainly include: spiral agitated tower type immersion machine, enhanced stirring pre-oxidation tank, thermometer, pH meter, air compressor, flow meter, cyanide and carbon adsorption tank.
(3) Test conditions
Grinding conditions: gold concentrate 2kg, water 2L, <37μm content 9915%, ambient temperature 30 ° C, ambient pressure 011 MPa, pulp concentration 50%.
Strengthen the alkali leaching pre-oxidation conditions (the pre-oxidation process has no preheating and heat preservation measures, NaOH is continuously added to maintain the pulp pH=11~12): slurry hydration 2L, pulp concentration 33%, temperature 30 °C, pressure 011 MPa, air pass The input amount is 013m3/h, the initiator No. 2 is 110kg/t, and the initial temperature of the slurry is 30°C.
Cyanide and carbon adsorption conditions: slurry CaO 80kg / t, pulp concentration 37% ~ 40%, pH ~ 11, temperature 30 ° C, time 24h.
Second, the results and discussion
(1) Fine grinding activation
Although the oxidation of arsenopyrite has a great thermodynamic trend, its natural oxidation reaction in water and air has a half-reaction period of 70 years, and the natural oxidation kinetics is very slow. Under the same conditions, the oxidative decomposition rate of arsenopyrite is about 4.5 times higher than that of pyrite. However, after fine grinding and activation, the thermal stability (melting point, decomposition temperature, reaction temperature, etc.) of the mineral is lowered, the acid and alkali resistance is weakened, the solubility, activity, reaction rate, etc. are improved, and the leaching reaction can be carried out under some high temperature and high pressure. It can occur under normal temperature and pressure.
The tower type grinding machine mainly uses grinding to grind, and has fine grinding ability and high efficiency. An important feature of this type of mill is that it has a strong mechanical activation while finely grinding the material, which can simultaneously strengthen and accelerate the chemical leaching process. Therefore, it is also an activator as an efficient fine grinding device, and can also be a pre-lead or pre-oxidizer.
As the fine grinding proceeds, the material is ground, increasing the specific surface area of ​​the material and the number of "live zones" of the reaction. Under certain grinding conditions, the degree of activation has a certain correspondence with the fineness of grinding. For the gold fine powder used in the test, the grinding fineness of 99.5% <37 μm can meet the requirements of the subsequent enhanced alkali leaching. This grinding fineness can be economically realized by using an industrialized TW type ultra-fine grinding tower type grinding machine.
(2) Strengthening alkali leaching pre-oxidation
The refractory gold fine powder is finely ground and activated by a tower type immersion machine, and then enters a fortified alkali immersion tank for pre-oxidation. Due to the enhanced mass transfer conditions, the surface of fresh, dissociated FeS and FeAsS particles is forcibly contacted with NaOH and O 2 ; the high shear rate removes the covering and rust spots on the surface of the particles, making the passivation or passivation film less late; Strong mass transfer conditions break or thin the diffusion interface layer, strengthen diffusion; and the alkali leaching reaction exotherm and other factors accelerate the oxidation rate of arsenic and sulfur minerals, and the following transformation occurs:
3AeAsS+9NaOH+4O 2 =Na 3 AsS 3 +2Na 3 AsO 4 +3Fe(OH) 3 (1)
4FeAsS+4FeS 2 +12NaOH+3O 2 +6H 2 O=4Na 3 AsS 3 +8Fe(OH) 3 (2)
2FeAsS+4NaOH+7O 2 =2Fe(OH) 3 +2Na 3 AsO 4 +2Na 2 SO 4 +2H 2 O (3)
2FeAsS+4NaOH+7O 2 =2FeAsO 4 +2Na 2 SO 4 +2H 2 O (4)
2FeAsS+4HaOH+3O 2 =2Na 2 S 2 O 3 +2Fe(OH) 2 (5)
Under certain conditions, Na 2 S 2 O 3 and Na 3 AsS 3 are further oxidized to Na 2 SO 4 and Na 3 AsO 4 , Fe(OH) 2 is oxidized to Fe(OH) 3 , and Fe(OH) 3 is decomposed. Into Fe 2 O 3 and the like.
Since FeAsS is thermodynamically more susceptible to oxidation than FeS 2 , it is always preferred to oxidize arsenopyrite in the pyrite-toxic sand community, indicating that the selectivity of oxidation can be achieved by utilizing the difference in oxidation rate of the arsenic sulfide mineral. In addition, due to the presence of gold in the mineral lattice, compositional changes, lattice distortions, dislocations, and other mineralogical reactions can be caused. Therefore, the oxidation distribution on the surface of the sulfide is also different, that is, the oxidation of the surface region is exhibited. Sex, so that FeS 2 is also selectively oxidized, accelerating the dissociation of gold. At the same time, due to the formation of thio salts, the consumption of NaOH is only a small fraction of the theoretical consumption of arsenic sulfur to arsenate and sulfate under the same oxidation rate.
As shown in Fig. 1, with the progress of stirring and strengthening alkali leaching, arsenic and sulfur minerals are rapidly oxidized, and the cyanidation leaching rate of the oxidized slag gold is gradually increased. Because gold concentrate has high sulfur content and low arsenic content, and gold is mainly wrapped by pyrite, the cyanide leaching rate of oxidation slag gold is positively correlated with the oxidation rate of sulfur. Preoxidation for 48h, sulfur oxidation rate of 87.50%, arsenic oxidation rate of 89.85%, oxidation leaching cyanide leaching for 24h, gold leaching rate of 85.85%. If the pre-oxidation time is extended, the recovery rate of cyanide leaching of the oxidized slag gold will continue to increase, but the power consumption and the cost of the chemical will also increase. There is an optimum balance between the pre-oxidation time and the gold leaching recovery rate, and the economic cost should not be neglected in pursuit of a high gold leaching rate. For the test materials, pre-oxidation for 48h can achieve the best match between technology and economy, meeting the mineralogical dissociation requirements of the immersible gold economy.
Figure 1 Sulfur and arsenic oxidation kinetics and corresponding gold cyanidation recovery
Strengthening the exothermicity of the alkali leaching reaction causes the temperature of the slurry to rise rapidly. The alkali leaching pre-oxidation is 0 to 1.75 h, and the slurry temperature rises rapidly from the initial 30 ° C to the peak point of 65 ° C. After 3 h of alkaline soaking, the slurry temperature was maintained at the level of 61 ° C for 3 h and then slowly decreased. At the end of the alkali leaching, the slurry temperature was 50 °C. The continuous release of the reaction heat during the enhanced alkali leaching process makes the slurry temperature much higher than the ambient temperature. This feature makes the process suitable for application in cold regions. During the enhanced alkali leaching process, the color of the slag changes rapidly. After alkali soaking for 1.5h, the material turned yellow obviously. When the alkali leaching ended, the material changed from the initial grayish black to dark brown. The precipitation reaction of Fe 3 + , Ca 2 + and AsO 4 3 - occurs during the simultaneous alkali leaching, so that most of the arsenic that has entered the liquid phase is transferred to the solid phase, and the solution contains only traces of arsenic.
At the same time of pre-oxidation, the slurry potential also changes accordingly, as shown in Figure 2. After stirring for 7 h, the slurry potential increased rapidly from the initial -843 mV to -247 mV, and then slowly increased, and the alkali leaching end point was -53 mV. This change law is actually an intuitive response to the oxidation process of the material. With the progress of enhanced alkali leaching, more and more sulfur and arsenic minerals are oxidized, and the ability of the pulp to be oxidized is gradually weakened, and its potential is inevitably gradually increased (sulfur arsenic and the like from a reduced state to an oxidized state). At the end of the alkali leaching, the material is converted from impregnable to easy to dip, making the extraction of gold easy.
Figure 2 Change in potential of pre-oxidized slurry
(3) Adding CaO pulping
After the alkali leaching, the CaO milk is added to adjust the slurry to precipitate the impurity ions in the solution, and the solution is purified, which facilitates the subsequent cyanidation gold extraction operation and reduces the cyanide consumption. At the same time, arsenic in the solution forms a calcium arsenate precipitate, which further reduces arsenic. If the amount of CaO added is appropriate, a part of the alkali may be regenerated. After filtration, the filtrate may be returned to the initial stage of alkali leaching or as a hydration water for evaporation of alkali due to alkali leaching during the alkali leaching process, and the alkali consumption is further reduced during recycling.
After the slurry is adjusted, the sedimentation and filtration properties of the solution are also greatly improved, which is easy to be filtered and settled, which is beneficial to the subsequent gold extraction operation and tailings pressure filter storage.
(4) Recycling of gold
The slurry after adding CaO milk is filtered, and the filter residue is further cyanated by adding new water. Figure 3 shows the cyanide leaching and adsorption kinetics of gold under the conditions of NaCN addition of 6 kg/t and activated carbon density of 17.5 g/L. After leaching and adsorption for 24 h, the recovery of cyanidation of gold was 85.85%, and the adsorption recovery was 99.62%.
Figure 3 Gold leaching and adsorption kinetics
Third, the conclusion
Using the mechanical activation of the ultra-fine grinding tower type immersion machine and strengthening the agitation of the alkali leaching pre-oxidation tank, the oxidation reaction of sulfur and arsenic minerals under high temperature and high pressure is initiated at normal temperature and pressure to cyanide a gold ore. The flotation concentrate of the tailings is converted from impregnable to easy to dip, and then the cyanidation and carbon adsorption operations are economically recovered. For cyanide tailings flotation concentrate containing gold grade 29.78 g / t, arsenic containing 0.64% and sulfur 19.90%, the recovery of cyanide leaching of gold after pre-oxidation is super-fine grinding-cyanide method before pre-oxidation The increase of 3.95 % to 85.85 % and the carbon adsorption rate of 99.62 %.
references
[1]Meng Yuqun. Pretreatment and thiosulfate leaching of re2fractory gold2bearing arsenosulfide concentrates [J]. Journal of University of Science and Technology Beijing , 2005, 12(5): 385 - 389.
[2] Meng Yuqun. A new extraction process of carbonaceous re2fractory gold concentrate [J]. Transactions of NonferrousMetals Society of China , 2005, 15(5): 1178 - 1184.
[3] Meng Yuqun, Dai Shujuan, Su Shaoling. Study on improving recovery rate of an arsenic-containing refractory gold ore[J]. Gold, 2005, 26(1): 34 - 36.
Author unit:
Institute of Metal Research, Chinese Academy of Sciences (Meng Yuqun)
Northeastern University (Dai Shujuan, Liu Dejun, Gao Fuqing)
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