Comprehensive recovery process and practice of cyanide tailings

I. Introduction

Most gold ores are associated with a variety of valuable elements silver, copper, lead, zinc, sulfur and the like. However, many gold mining companies tend to focus only on the recovery of gold, and the recovery rate of associated elements is generally low, resulting in waste of resources. With the decreasing of gold mineral resources, cyanide tailings have become a valuable secondary resource. How to economically and efficiently recover various valuable elements such as gold, silver, copper, lead and zinc and residual sodium cyanide in cyanide tailings has become an important content in the research and development of various gold mines. This will not only turn waste into treasure, generate economic benefits, but also reduce environmental pollution and produce good social benefits.

The cyanide tailings are tailings obtained by pressure filtration of flotation gold concentrate by cyanidation. Due to the nature of the ore and the gold extraction process, the properties, types and contents of valuable metals and minerals in the tailings are also There are different. Some of the main common features of cyanide tailings: mineral size is very fine, muddy is serious; mineral composition is more complex; contains a certain amount of CN one and some residual agents. Due to the above factors, the floatability of some minerals in cyanide tailings is greatly reduced, and it is difficult to recover valuable elements.

Most gold mines in China use flotation processes to treat cyanide tailings ^[1-4] . After flotation, the copper, lead, zinc and other minerals in the cyanide tailings are enriched and recovered, that is, the mineral resources are fully utilized, and good economic and social benefits can be achieved.

The Shandong Smelter Group Co., Ltd. smelter now produces gold and silver by cyanidation, and processes 250,000 tons of gold concentrate per year (self-produced and purchased). The cyanide tailings are sulfur concentrates and contain various non-ferrous metals such as copper, lead and zinc, with grades of 0.45%, 0.5% and 0.5% respectively. They have been sold as sulfur concentrates in the past. Before 2002, due to the weak chemical market, sulfur concentrates were unsalable for a long time. Because cyanide contains sodium cyanide and other chemical components, it inevitably causes pollution to both production and sales. In order to make full use of limited and non-renewable resources, the company has repeatedly researched and established the research topic of “clean production process and industrial application of comprehensive recovery of polymetallics from cyanide tailings”. In 1998, the company developed a technology for comprehensive recovery of gold, silver, copper, lead, zinc and other valuable metals and residual cyanide from cyanide tailings. In 2002, it invested 35 million yuan to build a recycling workshop, which was remarkable. Economic and social benefits.

2. Process mineralogy of cyanide tailings

The recovery of metals from cyanide tailings is different from the recovery of metals from ore.

(1) After the gold concentrate has been re-grinded and agitated for a long time, the mineral grain size is very fine (the content of -0.045mm grain size is 95% or even finer), and the specific surface is enlarged, showing a "colloidal" dispersion. The system makes separation of flotation difficult.

(2) The metal mineral is seriously over-grinded, and a part of the metal mineral is strongly inhibited due to excessive oxidation during cyanidation, and it is difficult to activate.

(3) A large amount of shale silicate minerals and cyanide in the pulp will deteriorate the flotation process and affect the grade and recovery rate of the concentrate.

The results of spectral analysis of cyanide tailings are shown in Table 1, and the results of chemical multi-element analysis are shown in Table 2.

Cyanide residue mainly metallic minerals chalcopyrite and pyrite, followed sphalerite and galena. Pyrite particles are triangular, cylindrical, elliptical, rectangular, and other irregular forms, ranging in size from a few microns to nearly one hundred microns, mostly at a few ten microns. The fracture characteristics of pyrite are obvious. Chalcopyrite is irregular in shape, ranging in size from a few microns to tens of microns, mostly on the order of a few microns. There is no mutual encapsulation of minerals in the cyanide residue, and the degree of dissociation is high.

Cyanide residue gangue mineral composition of quartz, sericite, calcite, feldspar, biotite. Quartz is the main gangue mineral with a mass fraction of 50% or more, irregular shape, and a particle size ranging from a few microns to 60 μm, mostly below 10 μm. The sericite has a particle size of up to 40 μm and is irregular in shape. The results of process mineralogical studies show that the cyanide residue contains a certain amount of Cu, Pb, and Zn elements, and can be separated by a suitable process.

Further comprehensive recovery of useful elements therein can be achieved.

Table 1 Cyanide slag spectral analysis results

Table 2 Results of multi-element analysis of cyanide residue

*w(Au)/10 ^-6 ,w(Ag)/10 ^-6

Third, the production process and indicators

Gold concentrates from cyanide treatment in smelters account for 65%, so the composition of gold concentrates is complex and unstable. The flotation ore is mainly composed of gold, silver and copper ore, gold, silver, copper, lead and zinc ore. The copper-bearing silver-gold concentrate and the lead-containing zinc-silver-gold concentrate obtained by flotation are mostly recovered after the cyanide-zinc powder replacement process. The grade of gold in tailings is generally 0.7-0.8/t, the grade of silver is about 15g/t, and the majority of copper-lead-zinc remains in cyanide tailings.

It is the key to recover valuable elements such as Cu, Pb, and Zn in cyanide tailings to achieve effective separation of various metals. According to the characteristics of cyanide tailings and the actual situation of the current market, the process and conditions of the products are Cu concentrate, Pb concentrate, Zn concentrate and PbZn mixed concentrate.

The cyanide tailings slag contains cyanide and lime, and the flotation separation of copper, lead and zinc is separated by virtue of their difference in characteristics after inhibition by cyanide and lime. Common chalcopyrite, porphyrite, chalcopyrite, pyrite, etc. are inhibited by cyanide and lime in alkaline solution after cyanidation leaching, poor floatability, weak inhibition of zinc minerals, lead minerals It is basically unchecked, and different minerals can be floated and separated by different flotation reagents. Combined with the complicated and unstable conditions of the sulfide mineralization in the gold concentrate treated by cyanidation, it is determined that two flotation test schemes are selected for the flotation separation test: the experimental scheme of Pb, Zn, Cu sequential flotation and Pb, Zn After the mixed selection, choose the Cu scheme.

Test carried out: direct cyanide tailings flotation flotation; cyanide tailings adjustment pH test; cyanide tailings directly adjusted to select Pb, adjust pH to select Zn; cyanide tailings selected Pb, Zn, Adding sulfuric acid to adjust pH=6~7 to select Cu test; after selecting cyanide tailings for Pb and Zn, adding sulfuric acid to adjust different pH values ​​to select Cu. The results of these tests show that there are two kinds of suitable cyanide tailings flotation process: one is Pb, Zn, Cu sequential flotation process; the other is Pb, Zn mixed selection and Cu process. The sorting index obtained in the first process: the recovery rate of Pb is 38.29%, the recovery rate of Zn is 65.88%, and the recovery rate of Cu is 50.41%. The sorting index of the second process: the recovery rate of Pb is 65.60%, the recovery rate of Zn is 70.90%, and the recovery rate of Cu is 75.48%. ,

Comprehensive comparison of the two processes, the second process is simpler than the first process, and the production cost is lower than the first process, easy to control, and the selection index is better than the former. At the same time, considering the market sales factors, the second process is chosen.

Based on the process selection test, the second process flow is used for design. The process mainly includes: cyanide tailings slurry, lead-zinc mixed flotation, sulfuric acid treatment, hydrocyanic acid recovery, copper flotation, flotation tailings dehydration, see Figure 1.

Figure 1 Process for recovering valuable elements from chlorinated tailings

First, the cleaned cyanide tailings are washed into a thickener for concentration. The underflow is filtered by a filter. The filter cake is added to the return water to adjust the concentration to the concentration of the slurry required for flotation. Then, sulfuric acid is added to adjust the pH of the slurry to make cyanide. Sodium sulphide inhibits copper without inhibiting lead and zinc, and performs lead-zinc mixed flotation. The flotation concentrate is selected and concentrated and filtered into lead-zinc concentrate, and the flotation tailings enters the acid leaching operation.

Lead-zinc mixed flotation tailings enter the acid leaching tank, add sulfuric acid for acid leaching, adjust the pH value to about 7, and the HCN gas formed by the action of sodium cyanide and acid in the pulp enters the absorption tower. In order to prevent environmental pollution, the method of vacuum pumping cyanide solution absorption is used to recover HCN gas, which effectively protects the environment. After the acid leaching of the slurry into the copper flotation, there is basically no sodium cyanide in the pulp, which has no inhibitory effect on the copper, so the copper concentrate can be obtained by flotation. The copper flotation tailings are concentrated and filtered, the filter cake is sold as a sulfur concentrate, and the filtrate is returned for recycling.

Fourth, the conclusion

(1) The comprehensive recovery process of valuable elements of cyanide tailings used in production, using cyanide in cyanide tailings to inhibit copper, lead and zinc minerals differently, preferentially mixing flotation lead, zinc and sulfuric acid Cyanide activates copper and sulfur, which not only improves the recovery of copper, but also recovers cyanide.

The main production equipment used for cyanide tailings treatment and recycling includes single-layer thickeners, plate and frame filter presses, flotation machines, leaching tanks and other common equipment, most of which are standard equipment, some of which are designed and manufactured by themselves, easy to select.

Material, easy to buy.

The main technical indicators of production are shown in Table 3.

Material consumption and other expenses are shown in Table 4.

Table 3 Main technical indicators

Table 4 Material consumption and other expenses

(II) The technical indicators achieved by the industrial application of the process are: lead grade of lead and zinc concentrate is 25.00%, zinc grade is 27.00%, lead recovery rate is 65.60%, zinc recovery rate is 70.90%; copper concentrate grade is 15.25%, the recovery rate is 75.48%; at the same time, it can be used as a by-product of gold and silver to achieve an annual increase of 32.2 million yuan.

(3) The long-term industrial application practice of the process shows that the process and conditions are selected reasonably and the indicators are stable. The entire production process is free of toxic and harmful waste water, waste slag and waste gas. The HCN gas is recovered by vacuum pumping cyanide solution to form regenerated sodium cyanide, which effectively protects the environment and achieves clean production.

[references]

[1] Yang Baocheng. Comprehensive utilization of flotation concentrate cyanide tailings [J]. Gold, 2004, 25 (3): 33-35.

[2] Wu Xiangyang, Wang Mingqin, Sun Shuping, et al. Research and application of clean production technology for recovery of lead-zinc mixed concentrate from cyanide tailings [J]. China Science and Technology Information, 2005 (17A): 172.

[3] Liang Guanjie. Comprehensive recovery of valuable metals in a cyanide tailings in Henan [J]. Comprehensive utilization of minerals, 001 (3): 35-37.

[4] Wang Hongjun. Experimental study and practice of polymetallic flotation of cyanide tailings [j]. Metal Mine, 2003 (7): 50-52.

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