No abstract

A novel pretreatment technique suitable for gold extraction from refractory ores was developed. The technique was based on selective arsenic fixing, using a fixing agent in the conventional two-stage roast. As in the existing fixing roast, more than 92 pct of the arsenic was retained in the calcine, using sulfate and lime as selective arsenic-fixing agents in fixing roast process. The arsenate retained in the leaching residue was found to be stable. The selective fixing of arsenic allowed about 80 pct of the sulfur to be recovered for sulfuric acid production. Compared to the existing fixing roast, the amount of fixing agent added was reduced, accompanied by a reduction in solid-waste generation. Integrated in a two-stage roast under the optimal operating conditions identified, the new process resulted in a gold recovery of 89 to 91 pct from a typical refractory gold ore containing a substantial amount of pyrite, arsenopyrite, antimony, and carbonaceous and organic carbons.

Sulfides with different distribution states may have different effects on steel properties. How to separately count each kind of sulfide remains a question. In the current study, sulfides in 1215 free‐cutting and 416 free‐cutting stainless steel are counted by Image‐Pro Plus image‐processing software. The sulfides can be divided into three categories, that is, cluster‐like sulfides, chain‐like sulfides, and individual sulfides. The features of each kind of sulfide are summarized and an automatic sulfide classification method is proposed. By using this method, sulfides in a metallographic photograph of 1215 steel are successfully classified into three types and counted separately. The quantity percentage of chain‐like, cluster‐like, and individual sulfides is 24.65%, 56.79%, and 18.56%, respectively, while the area percentage of different types of sulfides is 34.33%, 52.80%, and 12.87%. Individual sulfides have the highest‐quantity percentage of sulfides with a diameter smaller than 3 μm and with an area smaller than 10 μm2. Through this method, different types of sulfides can be deeply analyzed. It offers reliable data to evaluate whether the sulfides are well controlled or not, providing a guideline for the improvement of sulfide control methods.

No abstract