Of bauxite it comprises mainly a diaspore type, accounting for over 98% of the total reserves of bauxite, a mineral composed primarily of diaspore, kaolinite, illite and pyrophyllite. Due to the low aluminum-to-silicon ratio, the requirements of the Bayer process cannot be met, making the production cost of China's alumina industry significantly higher than the international level. Desiliconization by flotation is one of the effective ways to increase the aluminum to silicon ratio of bauxite. One of the key technologies for reverse flotation desiliconization is the selective inhibition of diaspore and enhanced recovery of silicate minerals. Therefore, the search for and development of selective flotation reagents is of great significance for the reverse flotation desiliconization of bauxite.
Starch is widely distributed in nature and is a rich and renewable macromolecular carbohydrate. Starch modifiers have been widely used, mainly for separation of hematite, magnetite and silicate minerals, such as iron oxide in the iron oxide mineral inhibiting reverse flotation process, also after the processing of starch It can better inhibit gangue minerals such as silicate and talc . In the desiliconization of bauxite reverse flotation, it has been tried to inhibit the diaspore with causticized starch, but it shows poor selectivity and weak inhibition ability. In this paper, the effect of anionic starch (LS-DZ) on the flotation behavior of silicate minerals was studied by flotation experiments. The results show that anionic starch has a good activation effect on flotation of silicate minerals and will promote aluminum-silicon minerals. Efficient separation.
I. Test materials and methods
   (1) Mineral sample
   Kaolinite was taken from Xiaoyi, Shanxi, and illite and pyrophyllite were taken from Wenzhou, Fujian. The lump ore is hand-broken, hand-selected and ground with a porcelain ball, and sieved out -0.074 +0.038mm for use. The purity of kaolinite, illite and pyrophyllite were 96.52%, 98.39% and 97.84%, respectively.
   (2) Single mineral flotation test
   The single mineral flotation test was carried out in an SFG hanging trough flotation machine. Each time, 3.0 g of mineral was weighed into a 40 mL flotation tank, distilled water was added, and the pH was adjusted with HCl or NaOH. After 2 minutes of slurrying, an anionic starch (LSDZ) and a collector DTAC were added, respectively, and the mixture was stirred for 3 minutes. Choose 4min. The foam product and the product in the tank are separately filtered, dried, weighed and the recovery rate is calculated. The test water is one distilled water.
   (III) Determination of adsorption amount
   Different concentrations of collector DTAC and anionic starch standard solution were prepared, and the absorbance was measured at a maximum absorption wavelength of 620 nm using a Shimadzu UV-3000 visible UV spectrophotometer to obtain a standard working curve. Take floating mineral slurry centrifuged and the supernatant was measured by absorbance measurement curve of the test conditions, whereby the residual dose in the pulp, and the amount of the agent adsorbed on the mineral surface calculated by subtraction.
   (4) Determination of zeta potential of mineral surface
   The ore sample was ground to -5 μm with an agate mortar, and 20 Mg each was weighed into a 100 mL beaker to prepare 0.04% pulp. The pH was adjusted with HCl or NaOH, and a certain concentration of anionic starch or DTAC was added or stirred, stirred on a magnetic stirrer, and the pH of the slurry was measured, and the potential was measured using a Coulter Delsa 440sx analyzer. Each sample was measured 3 times and averaged.
Second, the test results and discussion
   (1) Single mineral flotation test
   1, pH test
   The relationship between the flotation recovery of kaolinite, pyrophyllite and illite and the pH value of the slurry is shown in Figure 1 without adding or adding 10 mg/L anionic starch.
It can be seen from Fig. 1 that LSDZ has an activation effect on kaolinite, pyrophyllite and illite in the range of pH=4-11, and illite and pyrophyllite are more activated under weakly acidic conditions, and kaolinite. It can be well activated in the range of pH=4～9, and the recovery rate of kaolinite after activation is close to 100%.
2, anionic starch dosage test
The effect of the amount of anionic starch on the recovery of kaolinite, pyrophyllite and illite at pH=6 is shown in Fig. 2. It can be seen from Fig. 2 that when the amount of DTAC is 3×10 -4 mol/L, the amount of LSDZ is less than 10 mg/L and 40 mg/L, respectively, the flotation of activated kaolinite and illite increases with the amount of LSDZ. The recovery rate of kaolinite and illite is reduced, and mineral flotation is inhibited. When the amount of LSDZ is increased to 100 mg/L, the recovery rates of kaolinite and illite are reduced to 56% and 45%, respectively; The effect of LSDZ on the flotation of pyrophyllite is restricted by the amount of DTAC. When the amount of DTAC is 3×10 -4 mol/L, the addition of LSDZ inhibits the pyrophyllite flotation; when the amount of DTAC is 7×10 -4 mol/L, when the amount of LSDZ is less than 50 mg/L, the pyrophyllite is activated. Flotation, but as the amount of ISDZ increases, the flotation of pyrophyllite is inhibited. That is, under the suitable amount of collector, the low-amount anionic starch activates the flotation of three kinds of aluminosilicate minerals, which is beneficial to the separation of three minerals by reverse flotation.
(II) Determination of the adsorption amount of mineral surface
Fig. 3 is a graph showing the relationship between the adsorption amount of the cationic collector DTAC on the surface of the aluminum-silicon mineral and its concentration at pH=6. It can be seen from Fig. 3 that the adsorption amount of DTAC on the surface of illite minerals rises linearly at a lower concentration, and then the adsorption amount hardly changes with the increase of the concentration of the agent; the adsorption amount of DTAC on the surface of kaolinite and pyrophyllite begins with The increase in concentration rose quickly, and then the change was slow.
Figure 4 shows the effect of the amount of anionic starch on the adsorption capacity of DTAC on the surface of Al-Si minerals when pH=6 and DTAC dosage is 7×10 -4 mol/L. Combined with the results of Fig. 3, it can be seen from Fig. 4 that the adsorption of DTAC on the surface of kaolinite, illite and pyrophyllite is promoted at a low dosage of LSDZ. As the amount of LSDZ increases, the adsorption of DTAC on the mineral surface tends to be gentle.
(III) Results and analysis of mineral surface potential test
Figure 5 shows the effect of the agent on the zeta potential of illite, kaolinite and pyrophyllite at different pH conditions when the amount of DTAC is 3×10 -4 mol/L and the amount of LSDZ is 10 mg/L.
As can be seen from Figure 5, the isoelectric points of illite, kaolinite and pyrophyllite are about 2.0, 3.5 and 2.5, respectively. The trends of the effects of various agents on the surface zeta potential of the three minerals were similar.
The addition of anionic starch reduces the cardiac potential of the mineral surface. When the pH of the solution is lower than the isoelectric point of the mineral, the surface of the mineral is positively charged. The addition of anionic starch negatively shifts the potential, indicating that there is an electrostatic force between the anionic starch and the mineral; when the surface potential of the mineral is negative, the addition of starch makes Its potential continues to shift negatively, indicating that there is other force between starch and minerals. Studies have shown that when kaolinite is broken, it mainly dissociates along the interlayer, and there is residual hydrogen bonding force in the cleavage plane. Therefore, there is also a hydrogen bond between the anionic starch and the kaolinite.
Comparing the results of adding DTAC and adding ISDZ and DTAC, it can be seen that the potential of the mineral surface is more positive than that in the DTAC solution under the action of the two agents, indicating that the starch promotes the DTAC on the mineral surface. The adsorption is consistent with the adsorption test results and the flotation phenomenon.
Third, the conclusion
(a) Anionic starch has an activation effect on kaolinite, pyrophyllite and illite throughout the pH range. Under certain closed conditions, when the amount of anionic starch is low, kaolinite and illite are activated. With the increase of anionic starch dosage, kaolinite and illite are inhibited; the effect of anionic starch on the flotation performance of pyrophyllite is captured. The dosage of DTAC is limited.
(2) Both LSDZ and DTAC can be adsorbed on the surface of Al-Si minerals, and when the amount of LSDZ is low, the adsorption of DTAC on the surface of kaolinite, illite and pyrophyllite is promoted to different extents.
(3) The pH value of the pulp, the type and amount of the agent can affect the surface potential of the aluminosilicate mineral. The anionic starch negatively shifts the surface potential of the alumino-silicon mineral; the cationic collector DTAC shifts the surface potential of the alumino-silicon mineral; if the anionic starch and the cationic collector are added successively, the surface potential of the mineral is higher than that of the cation. The potential in the solution is further shifted positively, and the anionic starch promotes the adsorption of the collector on the mineral surface.
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