Electrochemical behavior of gold and its associated minerals in alkaline thiourea solutions

Electrochemical measurements were conducted to study the electrochemical behavior of gold （Au） and its commonly associated minerals in alkaline thiourea solutions. The results indicated that without addition of any stabilizer, selective dissolution of Au from stibnite and pyrite was only possible at relatively low thiourea concentrations. As Na2SiO3 was added, pyrite started to become active and an oxida- tion peak appeared; the oxidation peaks of axsenopyrite and chalcocite appeared earlier thaxl that of Au. The chalcocite peak shifted in the positive direction and the peak current increased. Stibnite did not show an oxidation peak and its current was nearly zero. Adding Na2SiO3 favored the selective dissolution of Au when its minerals were associated with chalcocite and stibinte. At pH 12, the Au anode dissolution peak current increased with stabilizer concentration. At 0.38 and 0.42 V and for Na2SiO3 concentration below 0.09 M, the current density continuously increased with Na2SiO3 concentration. The Na2SiO3 concentration had to be adequate to stabilize thiourea. When the potential was higher than 0.42 V, the surface of the Au electrode started to passivate. With an additional increase in potential, the presence of Na2SiO3 could not stop the inevitable decomposition of thiourea.

Comprehensive recovery of gold and base-metal sulfide minerals from a low-grade refractory ore

The comprehensive recovery of small amounts of valuable minerals such as gold and base-metal sulfide minerals from a low-grade refractory ore was investigated. The following treatment strategy was applied to a sample of this ore： gold flotation-gold concen- trate leaching-lead and zinc flotation from the gold concentrate leaching residue. Closed-circuit trials of gold flotation yielded a gold concen- trate that assayed at 40.23 g·t-1 Au with a recovery of 86.25%. The gold concentrate leaching rate was 98.76%. Two variants of lead-zinc flotation from the residue--preferential flotation of lead and zinc and bulk flotation of lead and zinc--were tested using the middling processing method. Foam from the reflotation was returned to the lead rougher flotation or lead-zinc bulk flotation, whereas middlings from reflotation were discarded. Sulfur concentrate was a byproduct. The combined strategy of flotation, leaching, and flotation is recommended for the treatment of this kind of ore.

Downregulation of serum CXCL4L1 predicts progression and poor prognosis in prostate cancer patients treated by radical prostatectomy

Our previous study found that plate factor-4 variant (CXCL4L1) was downregulated in the serum of patients with prostate cancer (PCa). The aim of the present study was to investigate the prognostic value of CXCL4L1 in PCa. In total, 213 PCa patients treated with radical prostatectomy were enrolled and peripheral blood samples of all patients were collected. Expression of serum CXCL4L1 in patients with different tumor stages and grades were measured by enzyme-linked immunosorbent assay (ELISA). The Kaplan-Meier method was applied to estimate the progression to castration-resistant prostate cancer (CRPC), metastasis, biochemical recurrenee (BCR)-free survival, and overall survival (OS). Prog no stic factors for BCR-free survival and OS were determi ned by univariate and multivariate analyses using the Cox proportional hazards regression model. The expression of CXCL4L1 was significantly lower in PCa patie nts with adva need pathological tumor stage, high-grade Gleason score, and metastasis. Moreover, down regulation of CXCL4L1 not only strongly correlated with aggressive clinicopathological features, but also predicted tumor progress!on and unfavorable outcomes. Finally, multivariate Cox regression analyses identified CXCL4L1 as an independent prognostic factor for both BCR-free survival (hazard ratio [HR]: 2.03, 95% confidence interval [Cl]: 1.26-3.27;P = 0.004) and OS (HR: 2.26, 95% Cl: 1.07-4.79;P= 0.033). In con elusion, our results in dicate that CXCL4L1 might serve as a no vel and promising prog no stic biomarker for patients with PCa and potential therapeutic target in the future.

Electrochemical dissolution behavior of gold and its main coexistent sulfide minerals in acid thiocyanate solutions

Electrochemical tests were developed to investigate the electrochemical dissolution behavior of gold and its main coexistent sulfide minerals in acid thiocyanate solutions.The optimal leaching conditions for gold in acidic thiocyanate system were pH 2,0.15 mol·L^(-1) thiocyanate and 0.2 g·L^(-1)Fe^(3+).Fe^(3+) addition to the acidic thiocyanate system promoted gold dissolution significantly,arsenopyrite dissolution was inhibited,chalcopyrite dissolution was increased,and the dissolution behavior of other associated minerals remained mostly unchanged.Thiocyanate made gold and associated mineral leaching easier.The galvanic corrosion effect of gold and its main coexistent sulfide minerals in an acidic thiocyanate-free system was that the chalcocite,arsenopyrite and pyrite acted as a cathode to reduce anodic gold dissolution;galena as an anode undergoes oxidation to inhibit anodic gold dissolution.There was almost no galvanic corrosion behavior between stibnite,yellow sphalerite and black sphalerite and gold.Thiocyanate addition changed the galvanic corrosion behavior of stibnite and yellow sphalerite in the thiocyanate system,which inhibited anodic gold dissolution.In the acidic thiocyanate system in the presence of ferric iron,the arsenopyrite promoted anodic gold dissolution,the chalcocite and gold were mostly free of galvanic corrosion,and the remaining minerals inhibited anodic gold dissolution.

Electrochemical adsorption and passivation on gold surface in alkaline thiourea solutions

An electrochemical method was used to examine Au surface absorption and passivation under the most commonly employed pH conditions in an alkaline Au leaching system.The polarization at different pH values was obtained through the current step curve.At pH 10,no absorption layer was formed.When the pH was increased to 11,an absorption layer was formed through the Au electrode reaction.At pH 12,the entire system could not be stabilized,even after long durations because of the thiourea oxidation and decomposition.The samples were analyzed by scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS),and atomic force microscopy(AFM).AFM observations of the Au plating surface and SEM-EDS analyses for the Au-coated graphite surface indicated that a passivation membrane was formed on the Au surface after its use in the alkaline thiourea Au leaching system.Two-step leaching was used to confirm the conclusions drawn from the experimental results.The twostage experimental results further confirmed the existence of a passivation membrane.