Research on resource comprehensive utilization of granite-type sulfide mine tailings

In order to recover and utilize mica and quartz from the tailings of a granite-type sulfide ore in Jiangxi Province, the technique of separating mica and quartz from the tailings by flotation without acid was investigated. Pyrite flotation was performed on a 500 g tailing sample to remove pyrite. And the middlings were acquired by desliming of the unfloated products. Finally mica and quartz was separated from the middlings in the mechanical flotation cell. Under conditions of pH=10.3 with a pulp concentration of 35% and a collector concentration of 180 g/t, a yield of 12.89% mica and 42.73% quartz was obtained, with silica grades as high as 71.50% in the quartz. The mica and quartz products can be used in construction ceramics and construction sand, respectively. It is believed that the outcomes of this work could provide ideas for comprehensive utilization of sulfide tailings.


Introduction
Mineral resources are an important material foundation for the country's economic construction and social development.With mineral processing developing, billions of tons of tailings are rejected as a major waste stream, which results in dramatical environment pollution and waste of resources [1][2][3] .China has a cumulative tailings stock of more than 20 billion tons, and annual production is growing at a rate of 1.2 billion tons.The direct soil pollution caused by tailings covers an area of over a million acres, while the indirect soil pollution covers an area of 667,000 hectares in China.For this reason, the implementation of waste-free discharge of tailings is required to maximize the utilization of mineral resources and protect the ecological environment [4,5] .Non-ferrous tailings are an important component of tailings, and most non-ferrous tailings are composed of mica, quartz, feldspar and other non-metallic minerals [6][7][8][9] .These components cannot be used effectively, resulting in low tailings consumption and a huge waste of resources.
Since 2015, a series of major decisions and deployments regarding the construction of green mines have been introduced in China, which vigorously promoted the full utilization of tailings, and strictly controlled the construction of new tailings ponds.Therefore, a comprehensive utilization of bulk nonmetallic resources in the tailings is imperative.At present, the comprehensive utilization of tailings consists of two main aspects: the recovery of useful minerals as secondary resources and the direct utilization of tailings by directly classifying them into one or several types of non-metallic ores for utilization without re-selection.
The main purpose of the work was to develop the core technology of separating mica and quartz in granite-type sulfide mine tailings under acid-free conditions in the laboratory, in order to achieve the purpose of tailings emission reduction

Experimental 2.1 Experimental materials
A run of granite-type sulfide mine tailings was obtained from a processing plant in Jiangxi province, China.Table .1 displayed the particle size composition of tailings.The XRD spectrum and phase compositions of the tailings were shown in Fig. 1 and Table .2. Table .1 illustrated that the proportion of -0.074 mm particles was 69.64%, of which -0.038 mm particles was 51.17%, indicating that the particle size distribution of the tailings was fine and the samples should be desliming.Fig. 1 displayed the samples contained principally quartz and mica, followed by small quantities of siderite, pyrite, chlorite, etc.The content of SiO 2 in the samples was low, while the content of Al and K elements were high.The chemical reagents, such as NaOH, HCl, xanthate, terpenic oil used in tests were obtained from Sinopharm Chemical Pharmaceutical Co. Ltd. (Shanghai, China).The BT-3 as a collector was synthetic.The water used for the tests was tap water.

Flotation tests 2.2.1 Pretreatment of granite-type sulfide tailings
The tailings samples contained some pyrite and the proportion of -0.0385 mm particles were high.Therefore, the samples were supposed to be pre-treated.Flotation flowchart was shown in Fig. 2. Flotation experiments were performed in an XDF-1000 machine at 1900 rpm to recover the valuable mineral from the tailings.First, 500 g of tailings samples and 900 mL of water were added to the cell and stirred for 3 min.The xanthate and terpenic oil were then added and stirred for 3 min.Flotation was performed for 6 min after pre-conditioning, and the floated (pyrite) products were received, filtered, and dried, while the unfloated products were deslimed.And the acquired slime was rejected and the middling was treated further.

Flotation separation of mica and quartz
Fig. 3 displayed the flowchart of flotation separation of mica and quartz.After desliming, the collector was added, and the pH of the pulp was adjusted to the experimental demand with NaOH or HCl and stirred for 4 min.Finally, the mica flotation was performed for 5 min, and the mica products and quartz products were recovered, filtered and dried.

Mica flotation 3.2.1 Influence of pH on the flotation results
The influence of pH on the flotation results of mica with BT-3 (240 g/t) as a collector was displayed in Table .3. As shown in Table .3, as the pH of the pulp increased from 9.0 to 10.8, the yield of mica continuously increased from 4.54% to 22.07%.And the grade of SiO 2 in the quartz product initially increased to 71.60% and then decreased to 69.48%.When the pH was increased to 10.3, the froth flotation phenomenon of mica was improved.What's more, the grade of SiO 2 in the quartz product was the highest, 71.60%.Taking all factors into consideration, the optimal flotation pH was determined to be 10.3.

Influence of pulp concentration on the flotation results
At pH 10.3, the effect of pulp concentration on the flotation yield of mica with BT-3 (240 g/t) as a collector was shown in Table .4. Table .4 showed an increase from 20% to 40% in the pulp concentration led to an increase from 9.81% to 17.41% in the yield of mica.As the flotation concentration exceeded 35%, the yield of mica remained relatively constant, but the amount of impurities in the mica products significantly increased.All things considered, the optimal pulp concentration for flotation was 35%.

Influence of collector dosage on the flotation results
At pH 10.3 and pulp concentration 35%, the influence of collector dosage on the flotation results was presented in Table .5. Table .5 illustrated the dosage of the collector had a significant impact on mica flotation.As the dosage of the collector increased from 60 g/t to 300 g/t, the yield of mica continuously increased from 5.89% to 17.78%, while the yield of quartz decreased from 49.41% to 36.91%, and the grade of quartz initially increased to 71.50% and then decreased to 70.86%.A little of collector dosage resulted in incomplete recovery of mica, leading to a higher content of impurities such as potassium and sodium in the subsequent quartz products.Excessive dosage of the collector not only affected the selectivity of flotation and increased costs but also led to the loss of quartz products.Based on this, the optimal dosage of the collector was determined to be 180 g/t, with a mica yield of 12.89% and a SiO 2 content of 71.50% in the quartz product.
Through the above tests, the optimal flotation flowchart of granite-type sulfide mine tailings was obtained in Fig. 5, by which pyrite products, mica products and quartz products with SiO 2 grade 71.50% could be acquired.Furthermore, these products could be used in their respective fields, as shown in Fig. 6.

Conclusion
1.The pH, pulp concentration, and collector concentration all have an impact on the flotation separation of mica and quartz, with the collector having the greatest influence.
2.At xanthate concentration of 50 g/t, pH of 10.30, pulp concentration of 35%, and BT-3 concentration of 180 g/t, the tailings of granite sulfide ore can be more effectively recovered and utilized through flotation.Through flotation, a yield of 17.66% of pyrite products, a yield of 12.89% of mica products, and a yield of 42.73% of quartz products can be obtained.The quartz product has the silica content of 71.50%.
3.The three products obtained from the experiment can all be applied in their respective fields.The research results provide ideas for comprehensive utilization and tailings reduction of granite-type sulfide tailings

Fig. 3
Fig.3 Flowchart of flotation separation of mica and quartz

Fig. 4
Fig.4 Pyrite flotation yield (a) and XRD spectrum of pyrite products (b) at different dosage of xanthate.

Table 1 .
Particle size composition of sulfide tailings Fig.1 XRD spectrum of tailings particlesTable.2Phase analysis of tailings

Table . 3
Test results of mica flotation at different pH

Table 4
Yield of mica at different pulp concentration

Table 5
Test results of flotation separation at different collector dosage