In the process of sulfuric acid production, the slag generated by roasting pyrite contains iron oxide and remaining ferrous sulfide, as well as a few components such as copper, lead, zinc, arsenic, and trace elements such as cobalt, selenium, germanium, silver, and gold. According to statistics, the amount of slag discharged in China in recent years is about 20 million tons, with a utilization rate of only 30%. The remaining slag not only occupies land but also pollutes the environment, and this trend is increasing year by year. Therefore, it has become an urgent task to induce the use of sulfuric acid slag, extract valuable components from it, and reduce waste residue emissions. This experiment takes a certain high-grade sulfur concentrate as the research objective, and discusses the optimal process conditions for roasting sulfur concentrate and leaching gold from slag, in order to achieve the intention of recovering iron and gold from slag and reducing waste discharge.
1、 Mineral sample properties
The chemical multi-element analysis of a high-grade sulfur concentrate is shown in Table 1. The sulfur concentrate has a high sulfur content of 51.6% and also contains low-grade gold, silver, copper, lead, zinc and other elements. The content of copper, lead, and zinc machining is low and cannot be summarized and recovered. The gold grade reaches 0.98g/t, which can be summarized and recovered.
According to the research results of sulfur concentrate technology and mineralogy, the composition of sulfur concentrate deposits is disorderly, mainly composed of sulfide deposits, and sulfide deposits are mainly composed of pyrite, with a small number of white iron and colloidal pyrite; Gangue mineral deposits include calcite, garnet, quartz, mica, etc. The degree of dissociation of individual sulfur deposits is relatively high, and the particle size of pyrite (white) in the connected bodies is relatively fine. Gold in sulfur concentrate is encapsulated in pyrite as ultrafine particles, which require treatment to dissociate and expose, in order to facilitate the leaching of gold. The sulfur concentrate was oxidized and roasted, and then gold was extracted to achieve the intention of induction and recovery.
2、 Process flow experiment
（1） Sulfur concentrate roasting experiment
1. Experiments on different roasting and insulation times
The roasting insulation time is 6, 7, 8, and 9 hours, and the roasting temperature is all 850 ℃. The experimental results show that under the condition of roasting temperature of 850 ℃, with the extension of insulation time, the yield of the slag decreases, but the grade of iron and gold in the slag continues to improve, while the sulfur content decreases rapidly. When the insulation time is 8 hours, the sulfur mass fraction decreases to 0.31%. Continuously adding insulation time, there is little change in the content of iron, gold plated audio power amplifier controller central control box shell, and sulfur, so the optimal insulation time is selected as 8 hours.
2. Baking temperature experiment
At the insulation time of 8 hours, under the conditions of roasting temperatures of 750 ℃, 850 ℃, and 950 ℃, the results of the roasting experiment were obtained
The experimental results and the chemical multi-element analysis results of the calcined slag indicate that at a calcination temperature of 850 ℃ and a holding time of 8 hours, the iron taste in the calcined slag is the highest, reaching 66.81%, with a gold grade of 1.31g/t and a sulfur content of 0.31%. The calcined slag has reached the requirements for qualified iron concentrate, and this temperature is within the temperature range of industrial pyrite calcination to produce sulfuric acid. Therefore, the calcination temperature is determined to be 850 ℃.
（2） Discussion on the Technology of Leaching Gold from Cinder
1. Experiment on sulfur removal from slag by water leaching
In order to summarize the recovery of gold from the slag, a gold leaching experiment was conducted. There is still residual sulfur in the calcined slag. In order to remove this sulfur, the slag is immersed in water. The experimental conditions for slag water immersion: the solid fraction of the water immersion solution is 2:1, and the immersion time is 15 minutes, respectively
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