Yongbin Yang

Co-intensification of cyanide leaching gold by mercury ions and oxidant

The effects of mercury ions on gold cyanidation were studied. The results show that under low cyanide concentration, gold cyanide process is controlled by CN(superscript -) transfer, while at higher cyanide concentration, there forms passivation on gold surface. Therefore, chemical oxidation of gold in cyanide solution of higher concentration is controlled by surface reaction. Small quantity of additions of mercury ions bring about great increases in anodic gold dissolution rate, decreases the passivation and reduces the equilibrium activated energy. In addition, they also markedly change the effect pattern of cyanide concentration. Mercury ions show positive effects on cathodic reduction of oxygen and raise the rate of electrochemical step of the cathodic reduction of oxygen. Addition of a certain amount of hydrogen peroxide is confirmed to be an effective way for intensification of cathodic process on gold electrode. Active potential range and current peak on anodic dissolution are enlarged when being co-intensified with Hg(superscript 2+) and hydrogen peroxide. Co-intensifying effect may be obtained and gold leaching rate is considerably increased on cyanide leaching of gold from gold concentrates.

Effect of arsenopyrite on thiosulfate leaching of gold

Abstract Arsenopyrite was artificially added into the thiosulfate leaching solution to clarify the role of arsenopyrite on the thiosulfate leaching of gold. The effect of arsenopyrite on the thiosulfate leaching of gold was studied by the thermodynamic calculation, mineral dissolution test, leaching test and XPS analysis. The results show that the thiosulfate consumption slightly increases with increasing the concentration of arsenopyrite, but the gold dissolution is obviously hindered. This may mainly attribute to the catalytic effect of arsenopyrite on the thiosulfate decomposition and the formation of passivation layer on the gold foil surface. The passivation layer likely consists of Cu2S or Cu(S2O3)35− element S, FeOOH and iron arsenate, which is deduced from the XPS analysis. However, the negative effect of arsenopyrite can be eliminated by adding additives. It is found that both additives of sodium carboxymethyl (CMC) and sodium phosphate (SHPP) can not only decrease the thiosulfate consumption but also improve the gold dissolution.

Thermodynamics of Reactions Among Al2O3, CaO, SiO2 and Fe2O3 During Roasting Processes

The thermodynamic of the chemical reactions among Al2O3, CaO, SiO2 and Fe2O3 in the roasting processes was investigated in this chapter. The chemical reactions are classified into SiO2-Al2O3 system, Fe2O3-Al2O3 system, SiO2-Fe2O3 system, CaO-Al2O3 system, SiO2-CaO system, SiO2-calcium aluminates system, CaO-Fe2O3 system, Al2O3-calcium ferrites system and Al2O3-CaO-SiO2-Fe2O3 system. When the roasting temperature is over 1100K, 3Al2O3·2SiO2 is preferentially formed in SiO2-Al2O3 system; FeO·Al2O3 can be formed in Fe2O3-Al2O3 system; ferric oxide and SiO2 could not generate iron silicate; 12CaO·7Al2O3 is preferentially formed in CaO-Al2O3 system when one mole Al2O3 reacts with CaO; 2CaO·SiO2 is preferentially formed in SiO2-CaO system; except for CaO·2Al2O3 and CaO·Al2O3, the other calcium aluminates can transform into calcium silicate by reacting with SiO2 in SiO2-calcium aluminates system; 2CaO·Fe2O3 is preferentially formed in CaOFe2O3 system; alumina is unable to form 3CaO·Al2O3 with calcium ferrites(2CaO·Fe2O3 and CaO·Fe2O3), but able to form 12CaO·7Al2O3 with 2CaO·Fe2O3; when CaO, Fe2O3, Al2O3,SiO2 coexist, they are more likely to form ternary compound 2CaO·Al2O3·SiO2 and 4CaO·Al2O3·Fe2O3.

Co-intensification of gold leaching with heavy metals and hydrogen peroxide

Abstract Co-intensification was researched to accelerate gold leaching with regards to its electrochemical nature by using anodic intensifiers of heavy metal ions (Pb 2+ , Bi 3+ , Tl + , Hg 2+ and Ag + ) on the basis of hydrogen peroxide assistant leaching on three different types of materials which were classified as a refractory sulphide gold concentrate, an easily leachable sulphide gold concentrate, and a low grade oxide gold ore according to their leaching characteristics. The results showed that, favorable co-intensification effects on the three materials were obtained and leaching time of gold was effectively shortened to no longer than 12 h from 16 to 24 h for hydrogen peroxide assistant leaching. For the five tested heavy metal ions, Bi 3+ and Tl + presented co-intensifying effect on all the three materials, and Hg 2+ caused co-intensifying effect on both refractory and easily leachable sulphide gold concentrates, and Pb 2+ and Ag + only had co-intensifying effect on the easily leachable sulphide gold concentrate.

Study on leaching Ti from Ti bearing blast furnace slag by sulphuric acid

Abstract The treatment for leaching Ti using sulphuric acid was investigated in order to utilise Ti bearing blast furnace slag including water quenched slag (WQS) and naturally cooled slag (NCS). Ti bearing blast furnace slag was subjected to direct agitation leaching with dilute sulphuric acid. Variables such as acid concentration, temperature, leaching time, liquid/solid ratio, particle size and stirring speed were studied. It was shown that, when WQS material (size range, 0–0·5 mm) was reacted with sulphuric acid of 50% concentration at a stirring speed of 400 rev min–1 with a liquid to solid weight ratio of 10 at 100°C for 1 h, Ti recovery from leaching was up to 72·3%. However, for NCS, Ti recovery was only ∼45% under comparative leaching conditions. A possible leaching mechanism and the difference of leaching effect between WQS and NCS are discussed. Unlike NCS, WQS is a type of activated slag, making it more favourable for extraction of Ti.

Extraction of manganese and zinc from their compound ore by reductive acid leaching

Abstract Comprehensive utilization of low grade manganese–zinc compound ore containing lead and silver with a method of reductive acid leaching was studied. According to the ϕ –pH diagram of Mn–Zn–H 2 O system, Mn and Zn can be leached simultaneously in the pH range of –2 to 5.61. The results showed that both hydrogen peroxide and sucrose were effective reductants which could intensify the simultaneous leaching of Mn and Zn into leachate as well as enrich Pb and Ag in the residue. 95.88% of Mn and 99.23% of Zn were extracted when the compound ore was leached with hydrogen peroxide in sulfuric acid media, meanwhile the contents of Pb and Ag in the residue were enriched to 13.21% and 489.36 g/t, respectively. When sucrose was used as the reductant, the leaching efficiencies of Mn and Zn separately achieved 98.26% and 99.62%, and contents of Pb and Ag in the residue were as high as 13.92% and 517.87 g/t, respectively.

Cohering Behavior of Iron Ore Pellet Powder in Kiln by a Novel Natural Stacking Method

The cohering behavior of iron ore pellet powder in kiln cannot be reflected entirely through the conventional briquetting method, so a novel natural stacking method was proposed in this paper. The results showed that in the two methods the cohering strength of powders from different iron ore pellets (numbered A, B and C) rose with the increase of roasting time and temperature and presented the same result, i.e., C > B > A. Comparatively, the natural stacking powders obtained much lower cohering strengths under the same roasting condition. The structure analyses of ring from the kiln tail and cohering briquette by the natural stacking method indicated that the occurrence of crystallized particles of them were extremely similar. Therefore, the initial information of pellet powder’s cohering behavior could be provided by the natural stacking method, improving the methods to study the actual ringing process and mechanism of pellet powders in kiln.

Extraction of Gold from a Low-Grade Double Refractory Gold Ore Using Flotation-Preoxidation-Leaching Process

The treatment process of a low-grade refractory gold ore containing sulfide minerals and carbonaceous matters was studied in this work. The gold extraction of this ore by all-sliming cyanidation was only 11.75%. Hence, a pretreatment was necessary. In this paper, a flotation-preoxidation-cyanide leaching process was developed. The concentrate from the flotation procedure was processed using different preoxidation methods. A concentrate containing 34.08g/t of gold with the gold recovery ratio of 81.20% was obtained by flotation. After roasting, microwave heating or alkaline pressure oxidation, the gold cyanidation ratio reached 82.37%, 81.26% and 71.09% respectively. Roasting was an effective, reliable and mature technique to oxidize sulfide minerals and carbonaceous matters. Roasting and microwave heating both produced dangerous environmental pollutants while alkaline pressure oxidation was eco-friendly.

Mechanism of Na2SO4 on Refractory Gold Concentrate at Roasting Pretreatment

It could significantly increase the leaching rate of refractory gold concentrate containing sulfur and arsenic by roasting pretreatment with adding certain amount of sodium sulfate, and the mechanism of that was systematically researched with DSC, XRD and SEM in this paper. Results indicated that the mechanism of Na2SO4 on double refractory gold concentrate at roasting pretreatment can be summed up in the following three aspects: Firstly, Na2SO4 can react with SO2 and SO3 which is produced by the oxidation of sulfides and generate Na2S2O7(l), which plays buffer effect on sulfides exothermic oxidation, avoiding the secondary-encapsulated of gold. Secondly, the liquid phase of Na2S2O7 can cover mineral particles’ surface that possesses a sintering effect, it leads to internal cracks of the particles. Finally, mineral particles will gather with sodium sulfate particles as the center that can improve the permeability of the layer.

Comparison of the Ringing Characteristics Between Acid and Alkaline Iron Ore Pellets Powder in Kiln

The ringing characteristics of acid and alkaline iron ore pellets powder in kiln were studied by the thermodynamic calculation using software FactSage7.0, roasting experiments using briquetting method and analysis of SEM-EDS. The thermodynamic calculation demonstrated that liquid phase could be generated from alkaline pellets powder at a lower temperature and the amount of formed liquid phase was much more than that from acid pellets powder at the same temperature. Roasting experiments indicated that the compression strength of alkaline pellets powder briquettes were also higher than that of acid pellets powder briquettes. Additionally, the analysis of SEM-EDS suggested that the alkaline pellets powder briquette presented more liquid phase and a more compact structure comparing with the acid pellets powder briquette, which was consistent with the results of thermodynamic calculation and roasting experiments. Hence, in comparison with acid pellets powder, alkaline pellets powder is much easier to ring in the kiln.