Investigation of the efficiency of using reagents from the class of oxidized modification of plant raw materials (oxidized polysaccharides) in the reverse flotation of nepheline

16.06.2022

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We publish a study provided by the Member of the Association "StekloSouz" of Russia JSC "Coralina Engineering".

Keywords: apatite-nepheline ore, current tailings of apatite flotation, recycled water, apatite, nepheline, feldspar, dark-colored minerals, nepheline concentrate, reverse flotation, magnetic separation, mass fraction, content, recovery, yield, froth product, chamber product, oxidized starch reagents from the class of modified vegetable raw materials.

The article presents the results of laboratory studies to identify the possibility of using oxidized polysaccharides from the class of modified plant materials as flotation reagents in the reverse flotation of nepheline. It is shown that these reagents provide a higher yield of nepheline concentrate and the extraction of Al2O3total into it at its standard quality. These new reagent modes make it possible to successfully carry out the process of reverse flotation of nepheline from a wide range of feed sizes, including in the presence of thin sludge. Such reagents can be successfully used at concentration plants enriching nepheline-containing ores.

The practice of nepheline production at Apatit JSC shows that nepheline concentrate at its processing plants was and is carried out by the method of reverse flotation of nepheline from apatite-nepheline ores after extraction from them by apatite flotation, i.e. from current apatite flotation tailings. In accordance with this technology, nepheline concentrate at Apatit JSC is obtained by direct flotation of dark-colored minerals, i.e. flotation extraction from apatite tailings into a frothy product of a whole range of minerals, such as titanomagnetite, pyroxenes, sphene, underextracted apatite and other minerals associated with them, while nepheline with feldspar is concentrated in the chamber product of flotation machines. This technology for obtaining nepheline concentrate has been successfully carried out for many decades, however, due to the fact that nepheline production at Apatit JSC is carried out under conditions of circulating water supply, and also considering that due to a significant deterioration in the quality of apatite-nepheline ores, and , therefore, a continuous increase in feldspars and dark-colored minerals in them is required to obtain a conditioned nepheline concentrate, adjusting the reagent formulation and the reagent regime of the reverse flotation of nepheline.

According to the existing technology, at the ANOF 3 apatite-nepheline plant, from the current apatite flotation tailings containing 22.0-23.0% Al2O3total, a high-quality nepheline concentrate is obtained with a mass fraction of Al2O3total - 28.5% with the extraction of 40-42% Al2O3total into it. The reverse flotation of nepheline at this plant is carried out by a fatty acid collector - crude tall oil (CTM) in a highly alkaline environment created by sodium hydroxide. The consumption of reagents used in flotation in this process is large and amounts to: crude tall oil - 1300-1500 g/t, NaOH - 500-800 g/t. Reverse flotation of nepheline is carried out under conditions of circulating water supply (80%) common with apatite production. Therefore, the high consumption of reagents used in the cycle for obtaining nepheline concentrate, as well as the high content of suspended solids in the liquid phase, has a very negative effect on the composition of recycled water and on the processes of flotation of apatite and nepheline as a whole.

In the current production of nepheline concentrate, before the reverse flotation of nepheline, it is planned to classify the current tailings of apatite flotation according to the class 0.16 mm and desludge them according to the class 0.040 mm, which leads to significant losses of the useful component, i.e. nepheline. In addition, as mentioned above, in recent years, the qualitative composition of processed apatite-nepheline ores and, accordingly, apatite flotation tailings has significantly deteriorated, as a result of which the content of pyroxenes (up to 15-17%) and feldspars (up to 8-12%) has increased. . As a consequence, there were difficulties in obtaining a traditional nepheline concentrate for the production of alumina. At the same time, the study of many research institutes, as well as the practice of the operation of apatite-nepheline factories, showed that the existing regime for separating dark-colored minerals from the tailings of apatite flotation is quite effective for them, but it is completely ineffective in the flotation of nepheline and feldspar. Therefore, a significant part of nepheline (especially fine particles) passes together with dark-colored minerals into a foam product (tails), reducing the extraction of nepheline into a chamber nepheline product. Therefore, for nepheline production, one of the main tasks is to find ways to increase the selectivity and efficiency of nepheline reverse flotation under conditions of circulating water supply.

In order to identify the possibility of improving the qualitative and quantitative indicators of the reverse flotation of nepheline on recycled water, laboratory studies were carried out using in this flotation process the products of oxidative modification of plant materials (oxidized starch reagents) obtained from various plant materials.

Modified vegetable raw materials contain basically vegetable polysaccharides, namely, starch modified with carboxyl groups, partially hydrolyzed protein, hydrolyzed fats and fiber. Therefore, it is of interest for use as a flotation reagent. Unlike flotation reagents prepared on the basis of pure starch, the new environmentally friendly reagent-modified vegetable raw materials use all its components: starch, proteins, fats, fiber, which ensures its specific properties, namely its versatility. Due to the synergistic effect that manifests itself with the optimal composition of such reagents, it is possible to increase the selectivity and efficiency of the flotation process.

The product of the reaction of oxidative modification of plant raw materials is obtained during its treatment with an alkaline solution in the presence of a catalyst, which is used as aqueous solutions of divalent copper compounds with constant stirring with simultaneous aeration. The process is carried out at a temperature of 70-75°C. Polysaccharides (subject to oxidation with the formation of carboxyl groups. As a result, a partial rupture of glucose bonds occurs with a decrease in the molecular weight of starch. As a result, the polysaccharide acquires high solubility in water, and aqueous solutions of salts and polymeric acids obtained from natural polysaccharides manifest themselves as highly effective surface- active substances.Under the action of alkali, fats and proteins are hydrolyzed with the formation of glycerol-like substances, salts of fatty acids and amino acids.Fiber in the presence of bases and copper compounds is oxidized by oxygen to carboxyl-containing derivatives.The final product is a suspension containing as a soluble part fatty acids, amino acids and carboxyl-containing derivatives of carbohydrates (in the form of salts) Suspensions can be dried using standard methods, and flotation reagents can be used both in dry form and in suspension form Such flotation reagents are environmentally friendly pure products, because belong to substances of IV hazard class. As plant raw materials for the production of oxidized polysaccharides, corn grains, rice flour, substandard grain seeds, millet and a number of other agricultural wastes can be used.

Reagents of this class are stable in saline solutions, and they are also resistant to calcium and magnesium aggression, which significantly expands their capabilities. The composition of such reagents, as mentioned above, includes starch modified with carboxyl groups up to 70%, partially hydrolyzed protein up to 15%, hydrolyzed fats up to 10% and fiber up to 5%. That is why a prerequisite for the use of these reagents in the process of reverse flotation of nepheline is their composition and, in particular, the presence of polyhydroxycarboxylic acids in them, which affect the selectivity of the flotation process.

To conduct research to identify the possibility of using modified polysaccharides for the reverse flotation of nepheline, the following samples were tested:

- OCR-1 reagent - a freshly prepared sample of an oxidized polysaccharide with a high degree of oxidation, obtained in the form of a suspension from substandard corn grains in industrial production (activity - 18.5%);

- reagent P-21 - a laboratory sample prepared from sifted rice flour and containing 70% fat and little starch (activity - 17.45%);

- reagent P-23 - a freshly prepared sample of oxidized polysaccharide with an average degree of oxidation, obtained from crushed corn grains (activity - 13.7%).

In laboratory studies, the following were used as feed for reverse nepheline flotation:

- current tailings of apatite flotation without regrinding and desliming, size - 0.3 mm;

- non-magnetic fraction isolated from the current tailings of apatite flotation with a size of -0.3 mm in a weak magnetic field;

- regrind (up to 100% to a fineness of 0.15 mm, 70% of the class -0.071 mm, current tailings of apatite flotation without desliming.

The granulometric characteristics of various nepheline reverse flotation feeds, on which the experiments were carried out, are shown in Table 1.

Table 1

Particle size distribution of apatite flotation tailings

From the above table it follows that the studied nepheline reverse flotation food products are characterized by different content of fine classes. At the same time, the largest amount of the 0.071 mm fraction is contained in the sample of tailings regrinded to 0.15 mm without subsequent desliming (70.1%), while in the current studied samples obtained without desliming and with partial desliming, the content of this class in them is lower by 7.6% and 16.7% respectively.

All types of nepheline reverse flotation feed were produced in the laboratory from apatite-nepheline ore containing 15.3% P2O5 and 14.5% Al2O3total and crushed to a fineness of 0.3 mm to isolate apatite from such ore.

The reverse flotation of nepheline was carried out according to the scheme, including the main flotation with preliminary contact of the feed with alkali (NaOH) - 2 min. and collector (STM) - 3 min.

The evaluation of the research results was carried out both according to the data of chemical analyzes of the enrichment products, and according to the main parameters of the control of the flotation process: pH, process speed, volume and destructibility of the foam formed at individual stages of the process. In addition to the above methods of control, when testing reagents, the separation efficiency index was calculated based on the results of chemical analyzes, which was calculated using the Hancock-Luyken criterion.

To conduct laboratory experiments on the reverse flotation of nepheline, circulating water was produced in the amount of 200 liters. During its development, experiments were first carried out on apatite flotation from apatite-nepheline ore crushed to a fineness of -0.3 mm in a laboratory flotation machine with a flotation chamber volume of 1 liter. The reagent mode of apatite flotation included a factory collecting mixture (250 g/t), the main components of which were distilled and crude tall oil, waste rock depressant - liquid glass (250 g/t) and ethoxylated alkylphenol (OP-4 - 10 g/t) . The liquid phase of the apatite flotation tailings obtained in the apatite flotation experiments and the filtrates after the treatment of the apatite concentrate with ferrous sulfate heptahydrate (1.0 kg/t of concentrate) were combined in a ratio of 4:1, after which this mixture in the form of mixed circulating water was used in the nepheline reverse flotation experiments . The composition of such recycled water is shown in Table 2.

Table 2

Mixed circulating water composition used in the reverse flotation of nepheline

At the first stage, studies on the study of the flotation properties of polysaccharides during the reverse flotation of nepheline were carried out on fresh distilled water using both the standard reagent regime and the use of modified starch reagents in the collecting mixture. The feed of the reverse flotation of nepheline in these experiments was the current tailings of apatite flotation without their regrinding and desliming. The results of these experiments showed that the efficiency of separation during the reverse flotation of nepheline according to the standard regime (NaOH - 610 g / t and OTM - 980 g / t) is very low even on fresh water, because separation efficiency criterion in this case did not exceed 11.79%. At the same time, in the chamber (nepheline) product, the mass fraction of Al2O3tot was 27.0%, with the extraction of Al2O3total into it 46.4%, and the yield of the chamber product was 37.2%. In the foam product, along with mafic minerals, a large amount of nepheline was extracted. So the extraction of Al2O3tot in this product was 53.56% with a content of 18.44% Al2O3total in it.In this case, as shown by mineralogical studies, about 96.0% of pyroxenes, 92.0% of titanomagnetite, almost 100% of sphene were extracted into the foam product and 57-58% of mica.However, due to the low efficiency of the separation of dark-colored minerals from nepheline with feldspar, 45.5 of the latter were extracted into the foam product, which led to large losses with it in the extraction of Al2O3total (53.56%).

With additional supply of OCR reagent (10 g/t) to the standard reagent regime of reverse flotation of nepheline, a significant change in the selectivity of this process occurs, the yield of the foam product decreases from 62.8 to 30.75% with a decrease in the mass fraction of Al2O3tot in it from 18.44% to 9.28%, in connection with which the loss of Al2O3total in extraction with the foam product decreases from 53.86% to 13.2%. At the same time, the yield of nepheline concentrate increased from 37.2 to 69.25% with the same quality (27.0-27.1% Al2O3total), which led to an increase in the extraction into nepheline concentrate from 46.40 to 86.8%, t .e. by 40.4% Al2O3tot. The separation efficiency coefficient in this case increased by 2 times and amounted to 22.39%.

The mineral analysis of the obtained products confirmed that in the case of the addition of the CSR reagent, the selectivity of the process increased sharply, since in the foam product, the mass fraction of nepheline and feldspar decreased from 45 to 12%. In addition, with the addition of the OCR reagent, the flotation rate increases, because flotation time reduced from 3 min. according to the standard mode up to 1.5 min. according to the regime with OKR.

The obtained results indicate the prospects of using modified polysaccharides for the reverse flotation of nepheline and the expediency of using such reagents under conditions of an increased content of fine sludge in the flotation pulp. Therefore, further studies were carried out on recycled water and various initial feeds. As recycled water, both the liquid phase of apatite flotation tailings and mixed recycled water were tested.

The results of these experiments showed that when nepheline was used for flotation with the traditional (standard) formulation of reagents (NaOH-610 g/t and OSTM-980 g/t), and as the recycled water of the liquid phase of the apatite flotation tailings, nepheline concentrate with a content of 27.55% Al2O3total when extracting 72.59% Al2O3total into it. The content of Al2O3tot in the froth product of the flotation machine was at the level of 15%. The efficiency criterion for the separation of minerals in this case is 17.3%. The addition of modified oxidized polysaccharides (OCR, R-21) to the traditional reagent mode in an amount of 1 to 15 g/t slightly improves the flotation process of reverse nepheline flotation. In these cases, the content of Al2O3tot in the nepheline concentrate was at the level of 27.30 to 28.05%, and the extraction of Al2O3total in them ranged from 75.46 to 79.41%, which is from 2.87% to 6.82% higher, than under standard conditions. The efficiency criterion for the separation of minerals in these experiments was approximately 20%, which is also higher than under standard conditions.

Due to the fact that the crude nepheline concentrate in these experiments was obtained substandard, but with a sufficiently high recovery, it was re-enriched using wet magnetic separation in a weak magnetic field, which ensured the production of high-quality nepheline concentrate from it containing more than 28.7 % Al2O3tot when extracting up to 64% Al2O3tot into it.

When conducting experiments on reverse nepheline flotation from current apatite tailings using mixed circulating water according to the traditional reagent regime (NaOH-610 g/t and OSTM - 980 g/t), a nepheline concentrate (chamber product) was obtained with a mass fraction of 27.64% Al2O3total when extracting 40.24% Al2O3total into it and a yield of 34.48%. The loss of Al2O3total with the foam product in these experiments was up to 60%. When feeding into the flotation process, in addition to the standard reagent regime, new reagents OKR and R-21 in an amount of 1 to 10 g/t, a nepheline concentrate was obtained containing up to 28.39% Al2O3total with the extraction of alumina into it at the level of 54.20%, which 14% more than the standard reagent mode.

A higher quality flotation nepheline concentrate was obtained by conducting reverse nepheline flotation from the non-magnetic fraction separated from the current apatite flotation tailings, i.e. without their regrinding and desliming in a weak magnetic field. These magnetic flotation experiments were carried out using mixed recycled water. The results of these studies showed that, according to the standard reagent regime, a flotation nepheline concentrate with a mass fraction of Al2O3total of 28.55% was obtained from the non-magnetic fraction of apatite flotation tailings containing 24.07% Al2O3tot, with the extraction of 34.96% Al2O3tot into it and a yield of 29.0% . When additionally from 1 to 5 g / t of reagents from the class of modified plant raw materials (OCR, R-21) are added to the OSTM collector, both the selectivity and the efficiency of the reverse flotation of nepheline increase, as a result of which the quality of the nepheline concentrate increases to 28.65-28 .8% of Al2O3total with a simultaneous increase in the extraction of Al2O3total into it up to 49.49%, i.e. by 14.56%. The output of the nepheline concentrate rises to 41.36%, i.e. by 12.36%.

In addition to the considered results of experiments on the reverse flotation of nepheline from current tailings of apatite flotation with a size of -0.3% with the identification of the feasibility of using reagents from the class of modified raw materials in the collection mixture, similar studies were also carried out on current apatite tailings regrinded to a fineness of -0.15 mm. In these experiments, the reverse nepheline flotation feed contained 62.5% -0.071 mm class, and the liquid phase of the apatite flotation tailings and mixed reverse water were used as recycle water. The results of these studies showed that when carrying out the reverse flotation of nepheline in the presence of slimes from finely divided material according to the standard regime, a nepheline (chamber) product was obtained containing 27.9–28.2% Al2O3total with the extraction of 62.23% Al2O3total into it. When oxidized polysaccharides (OCR, R-21) were introduced into the pulp before conditioning with a collector (OSTM-980 g/t) in an amount of 1-2 g/t, a higher quality nepheline concentrate (28.4-28.6 Al2O3total) was obtained at increasing its extraction into concentrate up to 69.17-74.2%, i.e. by 6.8-12.02%. The separation efficiency in this case was 18.49%.

Similar results were obtained for the reverse flotation of nepheline from finely ground initial apatite tailings using mixed recycled water and new modified starch-containing reagents in this process, i.e. oxidized polysaccharides. Experiments have shown that when using the above reagents (OCR and R-21) together with the collector OSTM in an amount of 2 to 4 g / t, conditioned nepheline concentrates were obtained containing 28.55-28.65% Al2O3total with an extraction of 69% Al2O3tot.

Thus, the conducted studies have established that oxidized polysaccharides have a positive effect on the selectivity and efficiency of the reverse flotation of nepheline under conditions of a closed water cycle, and, therefore, such reagents can be recommended for use in the corresponding processing plants.

The data obtained make a significant contribution to the study of the enrichment of nepheline ores. For a more detailed establishment of regularities, as well as for tracking the dynamics of enrichment of nepheline ores from different deposits, further research will be carried out in our Mineral Research Center.