Extraction of Phosphorous from a Phosphorous-Containing Vanadium Titano-Magnetite Tailings by Direct Flotation

: In this study, there is 1.42% P 2 O 5 in the P-containing V-Ti magnetite tailings in Miyi Region of China, with the valuable minerals mainly including apatite, and aluminosilicate minerals as the main gangue components. The direction ﬂotation process was used to recover phosphorous from the low-grade phosphorous-bearing V-Ti magnetite tailings. The results showed that an optimized phosphorous concentrate with a P 2 O 5 grade of 31.35% and P 2 O 5 recovery of 88.02% was obtained by ﬂotation process of one roughing, three scavengings, and three cleanings under roughing conditions, which employed pulp pH of 9, grinding ﬁneness of < 0.039 mm occupying 90%, ﬂotation concentration of 25%, and dosages of carboxymethylcellulose, oxidized para ﬃ n wax soap, and pine oil of 400 g / t, 300 g / t, and 20 g / t, respectively. Optimized one scavenging, two scavenging, and three scavenging conditions used a pulp pH of 9, and dosages of carboxymethylcellulose, oxidized para ﬃ n wax soap, and pine oil of 200 g / t, 150 g / t, 10 g / t; 100 g / t, 75 g / t, and 5 g / t; and 100 g / t, 75 g / t, and 5 g / t, respectively. Optimized one cleaning, two cleaning, and three cleaning condition dosages of carboxymethylcellulose of 100 g / t, 50 g / t, and 25 g / t, respectively. Study of analysis and characterization of phosphorous concentrate by X-ray di ﬀ raction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) show that most gangue minerals enter the ﬂotation tailings, the main minerals in phosphorous concentrate are apatite, olivine, and feldspar. the P 2 O 5 grade of phosphorus concentrate decreased from 13.66% to 12.05%, and the P 2 O 5 recovery rate increased from 59.80% to 66.28%.When the dosage of oxidized para ﬃ n soap ranged from 400–600 g / t, the P 2 O 5 grade of phosphorus concentrate decreased from 10.65% to 7.56%, and the P 2 O 5 recovery increased from 66.62% to 69.34%. It shows that increasing the amount of collector is beneﬁcial to improving the separation index of phosphate concentrate, but too much is not conducive to the ﬂotation of phosphate minerals, and other minerals are easy to be ﬂoated, thus a ﬀ ecting the quality of concentrate products. Therefore, oxidized para ﬃ n soap dosage of 300 g / t is reasonable, and phosphorous concentrate with a P 2 O 5 grade of 12.05% and P 2 O 5 recovery of 66.28% was obtained.


Introduction
Phosphorus is an important non-metallic mineral resource, which is widely used in agriculture, chemical industry, medicine, food, and other industrial sectors. The global phosphate mineral resources are very rich, but the distribution is extremely uneven, among which the phosphate mineral reserves in Morocco and Western Sahara, China, and Syria account for more than 80% of the total proved phosphorus reserves in the world. With the continuous exploration and development of global phosphate ore, high grade of P 2 O 5 and low harmful impurities of high-quality phosphate ore resources are gradually decreasing, the overall development of global phosphate ore resources is developing towards the direction of low-quality phosphate ore resources [1].
Processes 2020, 8,874 3 of 16 minerals, the content of phosphate minerals in tailings will be further reduced, which can reduce the pollution of soil caused by phosphorus in tailings. At the same time, the comprehensive utilization of phosphorus can effectively promote the new round of research on associated valuable elements in the Miyi region of China, and has a certain promoting effect on improving the comprehensive utilization process of V-Ti magnetite resources [15][16][17][18][19].

Sampling
The ore samples used in this study were from a low-grade phosphorus-containing vanadium titano-magnetite tailings produced by a concentrator in Miyi region after recovering iron and titanium using magnetic separation and flotation. The particle size was between 0.019 and 3.0 mm. It was found that the blend ore samples were all caused by fine-grained caking. In order to ensure that the sample is representative, the agglomerated samples were crushed and then shrunk in advance for reserve. The main chemical composition analysis of the P-bearing V-Ti magnetite tailings is shown in Table 1, and the grain size analysis of the samples is shown in Table 2. The main mineral composition of the P-bearing V-Ti magnetite tailings is shown in Figure 1. The content of silicoaluminate mineral is higher, and the main minerals contain apatite, hornblende, feldspar, serpentine, chlorite, mica, quartz, dolomite, and calcite in the vanadium titano-magnetite tailings. same time, the comprehensive utilization of phosphorus can effectively promote the new round of research on associated valuable elements in the Miyi region of China, and has a certain promoting effect on improving the comprehensive utilization process of V-Ti magnetite resources [15][16][17][18][19].

Sampling
The ore samples used in this study were from a low-grade phosphorus-containing vanadium titano-magnetite tailings produced by a concentrator in Miyi region after recovering iron and titanium using magnetic separation and flotation. The particle size was between 0.019 and 3.0 mm. It was found that the blend ore samples were all caused by fine-grained caking. In order to ensure that the sample is representative, the agglomerated samples were crushed and then shrunk in advance for reserve. The main chemical composition analysis of the P-bearing V-Ti magnetite tailings is shown in Table 1, and the grain size analysis of the samples is shown in Table 2. The main mineral composition of the P-bearing V-Ti magnetite tailings is shown in Figure 1. The content of silicoaluminate mineral is higher, and the main minerals contain apatite, hornblende, feldspar, serpentine, chlorite, mica, quartz, dolomite, and calcite in the vanadium titano-magnetite tailings.

Flotation Reagent and Equipment
The main chemical reagents used in this experiment are oleic acid, oxidized paraffin soap, hydroximic acid, benzyl arsenic acid, sodium bicarbonate, lime, sodium carbonate, sodium hydroxide, sodium hexametaphosphate, carboxymethylcellulose (CMC), sodium fluosilicate, and sodium silicate, all of which have analytical purity and a producing area Shanghai AiBi Chemistry Preparation Co., Ltd., Shanghai, China.

Procedure Design
Flotation (roughing, scavenging), aimed at increasing the P 2 O 5 grade and phosphorous recovery of phosphorous concentrate, was carried out using an XFD-1.5 L hanging tank flotation operating at a spindle speed of 1650 r/min. A 500 g mass of phosphorous containing vanadium-titanium magnetite tailings was added to the 1.5 L flotation tank. Flotation (cleaning), aimed at increasing the P 2 O 5 grade of phosphorous concentrate, was carried out using an XFD-1.0 L hanging tank flotation machine (Jinlin Exploration Machinery Plant, Changchun, China) operating at a spindle speed of 1650 r/min. A 200-300 g mass of phosphorous concentrate was added to the 1.0 L flotation tank. Distilled water (1.0 L) was added and the pulp stirred and mixed for about 3 min, followed by adjustment to the required pH using NaOH, NaHCO 3 , CaO, or Na 2 CO 3 . After 5-10 min of pulping, the depressants were added to the slurry and conditioned for about 3 min. Then, the collectors for improving phosphorous grade and recovery were added and agitated for about 3 min. Before aeration, the frothers (pine oil) for improving the bubble were added, with another about 3 min of stirring. After about 3 min of flotation, the froth (phosphorous concentrate) and in-tank product (flotation tailings) were separately filtered, dried at 85 • C for 1.5-2 h, and weighed. Quantitative analyses of phosphorous grade were conducted to calculate the phosphorous recovery. Calculation of the phosphorus recovery is shown in Equation (1).
where, Q 1 is the weight of phosphorus concentrate/g, Q 2 is the weight of flotation tailings/g, β 1 is the P 2 O 5 content of phosphorus concentrate/%, and β 2 is the P 2 O 5 content flotation tailings/%.

Analysis and Characterization
The chemical composition of P-containing vanadium titano-magnetite tailings, phosphorus concentrate, and flotation tailings was analyzed by a Z-2000 atomic absorption spectrophotometer (Hitachi Co., Ltd. Tokyo, Japan). The mineral phase compositions of P-containing vanadium titano-magnetite tailings, phosphorus concentrate, and flotation tailings were analyzed by X-ray diffraction (XRD, X Pert pro, Panaco, The Netherlands). The microstructure of the solid products was observed by SEM (S440, Hirschmann Laborgerate GmbH & Co. KG, Eberstadt, Germany) equipped with an energy-dispersive X-ray spectroscopy (EDS) detector (UItra55, CarlzeissNTS GmbH, Hirschmann Laborgerate GmbH & Co. KG, Eberstadt, Germany).

Effect of Different Collectors
The commonly used collectors for phosphate ore flotation include oleic acid, sodium oleate, oxidized paraffin soap, hydroxamic acid, and benzyl arsenate, among which oleic acid, sodium oleate, oxidized paraffin soap, and other fatty acid collectors have a wide range of sources, low price, mild reaction conditions, and can achieve phosphate mineral flotation under alkaline conditions. Oxidized paraffin soap (RCO 2 Na) contains more than C 18 -C 32 long chain fatty acids, and can form complexes on the surface of various mineral metals, which can greatly improve the hydrophobicity of the mineral surface, and at the same time have foaming property, so it can replace anion harvesters of various fatty acid soaps and be used in the flotation of various mineral products. Hydroxyl oxime arsenic acid and benzyl arsenic acid contain a toxic element and have strong foaming performance, then in the process of flotation test, we found that when the flotation foam is bigger with more viscosity, the water content is high, which eventually led to the foam product of phosphorus grade and recovery index was not ideal [20][21][22].
Results in Figure 2 reveal that the selectivity of oleic acid in the flotation process is relatively poor, which also leads to the lower phosphorus grade and recovery of the obtained flotation phosphorus concentrate. Oleic acid, oxidized paraffin soap, hydroxamic acid, and benzyl arsenic acid can realize the flotation of phosphate minerals. The flotation effect of oxidized paraffin soap as a collector is the most obvious, and phosphorus concentrate with a P 2 O 5 grade of 12.65%, and P 2 O 5 recovery of 65.31% can be obtained. Therefore, oxidized paraffin is suitable as a flotation collector. oleate, oxidized paraffin soap, and other fatty acid collectors have a wide range of sources, low price, mild reaction conditions, and can achieve phosphate mineral flotation under alkaline conditions. Oxidized paraffin soap (RCO2Na) contains more than C18-C32 long chain fatty acids, and can form complexes on the surface of various mineral metals, which can greatly improve the hydrophobicity of the mineral surface, and at the same time have foaming property, so it can replace anion harvesters of various fatty acid soaps and be used in the flotation of various mineral products. Hydroxyl oxime arsenic acid and benzyl arsenic acid contain a toxic element and have strong foaming performance, then in the process of flotation test, we found that when the flotation foam is bigger with more viscosity, the water content is high, which eventually led to the foam product of phosphorus grade and recovery index was not ideal [20][21][22]. Results in Figure 2 reveal that the selectivity of oleic acid in the flotation process is relatively poor, which also leads to the lower phosphorus grade and recovery of the obtained flotation phosphorus concentrate. Oleic acid, oxidized paraffin soap, hydroxamic acid, and benzyl arsenic acid can realize the flotation of phosphate minerals. The flotation effect of oxidized paraffin soap as a collector is the most obvious, and phosphorus concentrate with a P2O5 grade of 12.65%, and P2O5 recovery of 65.31% can be obtained. Therefore, oxidized paraffin is suitable as a flotation collector.

Effect of Oxidized Paraffin Soap Dosage
In the process of flotation, the function of the collector is to strengthen the mineral adhesion to the foam, so as to change the hydrophobicity of the mineral surface, so as to realize the purpose of the mineral entering the flotation foam and becoming the concentrate product [23][24][25].
It is known from Figure 3 that the amount of oxidized paraffin soap can improve the flotation index of phosphorus concentrate. When the amount of oxidized paraffin was in the range of 100-300 g/t, the P2O5 grade of phosphorus concentrate decreased from 13.66% to 12.05%, and the P2O5 recovery rate increased from 59.80% to 66.28%.When the dosage of oxidized paraffin soap ranged from 400-600 g/t, the P2O5 grade of phosphorus concentrate decreased from 10.65% to 7.56%, and the P2O5 recovery increased from 66.62% to 69.34%. It shows that increasing the amount of collector is beneficial to improving the separation index of phosphate concentrate, but too much is not conducive to the flotation of phosphate minerals, and other minerals are easy to be floated, thus affecting the quality of concentrate products. Therefore, oxidized paraffin soap dosage of 300 g/t is reasonable, and phosphorous concentrate with a P2O5 grade of 12.05% and P2O5 recovery of 66.28% was obtained.

Effect of Oxidized Paraffin Soap Dosage
In the process of flotation, the function of the collector is to strengthen the mineral adhesion to the foam, so as to change the hydrophobicity of the mineral surface, so as to realize the purpose of the mineral entering the flotation foam and becoming the concentrate product [23][24][25].
It is known from Figure 3 that the amount of oxidized paraffin soap can improve the flotation index of phosphorus concentrate. When the amount of oxidized paraffin was in the range of 100-300 g/t, the P 2 O 5 grade of phosphorus concentrate decreased from 13.66% to 12.05%, and the P 2 O 5 recovery rate increased from 59.80% to 66.28%.When the dosage of oxidized paraffin soap ranged from 400-600 g/t, the P 2 O 5 grade of phosphorus concentrate decreased from 10.65% to 7.56%, and the P 2 O 5 recovery increased from 66.62% to 69.34%. It shows that increasing the amount of collector is beneficial to improving the separation index of phosphate concentrate, but too much is not conducive to the flotation of phosphate minerals, and other minerals are easy to be floated, thus affecting the quality of concentrate products. Therefore, oxidized paraffin soap dosage of 300 g/t is reasonable, and phosphorous concentrate with a P 2 O 5 grade of 12.05% and P 2 O 5 recovery of 66.28% was obtained.

Effect of Different Depressants
The main gangue minerals in the vanadium titanium magnetite tailings contain mica, feldspar, chlorite, hornblende, and other silica-aluminate minerals. The common depressants of gangue minerals are sodium silicate, sodium hexametaphosphate, sodium fluorosilicate, and carboxymethyl cellulose. The results in Figure 4 show that the addition of carboxymethyl cellulose as an inhibitor is the most obvious to improve the quality of phosphorus concentrate. Carboxymethylcellulose molecule is composed of a number of glucose units, each unit of glucose with three base, namely in the C2 and C3 position para hydroxy and primary hydroxyl in C6 location, and the base to compare live dial by the base of the extent of the hydrogen atoms are replaced by carboxymethyl called substitution degree, the higher the degree of substitution of spindle methyl cellulose charged, the more easily dissolved in the aqueous solution. In aqueous solution, carboxymethylcellulose or ionization which makes its molecular burden on electric carboxymethylcellulose with slurry surface, make the slime superficiality magnesium silicate minerals which are the main gangue mineral, this kind of ore including serpentine, hornblende, and olivine changes, thereby corresponding inhibition [26][27][28][29].
Therefore, the highest P2O5 recovery of phosphate concentrate obtained by sodium hexametaphosphate as a depressant was 73.92%, and the highest P2O5 grade of carboxymethyl cellulose as an inhibitor of phosphate concentrate was 18.26%. After comprehensive consideration, phosphorous concentrate with a P2O5 of 18.26% and P2O5 recovery of 70.79% can be obtained by selecting carboxymethylcellulose as the depressant of the flotation process.

Effect of Depressant Dosage
The purpose of adding carboxymethylcellulose is to enhance the hydrophilicity of gangue minerals, weaken the effect between the gangue minerals and the collectors, and, thus, to strengthen Recovery (%) 13

Effect of Different Depressants
The main gangue minerals in the vanadium titanium magnetite tailings contain mica, feldspar, chlorite, hornblende, and other silica-aluminate minerals. The common depressants of gangue minerals are sodium silicate, sodium hexametaphosphate, sodium fluorosilicate, and carboxymethyl cellulose. The results in Figure 4 show that the addition of carboxymethyl cellulose as an inhibitor is the most obvious to improve the quality of phosphorus concentrate. Carboxymethylcellulose molecule is composed of a number of glucose units, each unit of glucose with three base, namely in the C 2 and C 3 position para hydroxy and primary hydroxyl in C 6 location, and the base to compare live dial by the base of the extent of the hydrogen atoms are replaced by carboxymethyl called substitution degree, the higher the degree of substitution of spindle methyl cellulose charged, the more easily dissolved in the aqueous solution. In aqueous solution, carboxymethylcellulose or ionization which makes its molecular burden on electric carboxymethylcellulose with slurry surface, make the slime superficiality magnesium silicate minerals which are the main gangue mineral, this kind of ore including serpentine, hornblende, and olivine changes, thereby corresponding inhibition [26][27][28][29].

Effect of Different Depressants
The main gangue minerals in the vanadium titanium magnetite tailings contain mica, feldspar, chlorite, hornblende, and other silica-aluminate minerals. The common depressants of gangue minerals are sodium silicate, sodium hexametaphosphate, sodium fluorosilicate, and carboxymethyl cellulose. The results in Figure 4 show that the addition of carboxymethyl cellulose as an inhibitor is the most obvious to improve the quality of phosphorus concentrate. Carboxymethylcellulose molecule is composed of a number of glucose units, each unit of glucose with three base, namely in the C2 and C3 position para hydroxy and primary hydroxyl in C6 location, and the base to compare live dial by the base of the extent of the hydrogen atoms are replaced by carboxymethyl called substitution degree, the higher the degree of substitution of spindle methyl cellulose charged, the more easily dissolved in the aqueous solution. In aqueous solution, carboxymethylcellulose or ionization which makes its molecular burden on electric carboxymethylcellulose with slurry surface, make the slime superficiality magnesium silicate minerals which are the main gangue mineral, this kind of ore including serpentine, hornblende, and olivine changes, thereby corresponding inhibition [26][27][28][29].
Therefore, the highest P2O5 recovery of phosphate concentrate obtained by sodium hexametaphosphate as a depressant was 73.92%, and the highest P2O5 grade of carboxymethyl cellulose as an inhibitor of phosphate concentrate was 18.26%. After comprehensive consideration, phosphorous concentrate with a P2O5 of 18.26% and P2O5 recovery of 70.79% can be obtained by selecting carboxymethylcellulose as the depressant of the flotation process.

Effect of Depressant Dosage
The purpose of adding carboxymethylcellulose is to enhance the hydrophilicity of gangue minerals, weaken the effect between the gangue minerals and the collectors, and, thus, to strengthen

Recovery (%)
Oxidized paraffin soap dosage: 300 g/t Pine oil: 20 g/t pH: 8 (adjusting by sodium hydroxide) Grinding fineness: ＜0.045 mm occupying 90% Floatation concentration: 25% Therefore, the highest P 2 O 5 recovery of phosphate concentrate obtained by sodium hexametaphosphate as a depressant was 73.92%, and the highest P 2 O 5 grade of carboxymethyl cellulose as an inhibitor of phosphate concentrate was 18.26%. After comprehensive consideration, phosphorous concentrate with a P 2 O 5 of 18.26% and P 2 O 5 recovery of 70.79% can be obtained by selecting carboxymethylcellulose as the depressant of the flotation process.

Effect of Depressant Dosage
The purpose of adding carboxymethylcellulose is to enhance the hydrophilicity of gangue minerals, weaken the effect between the gangue minerals and the collectors, and, thus, to strengthen the separation of gangue minerals from apatite. Increasing the dosage of carboxymethylcellulose is beneficial to improving P 2 O 5 grade and recovery of phosphorus concentrate.
The test results in Figure 5 show that the appropriate addition of carboxymethylcellulose as an inhibitor can improve the effect of phosphorus flotation; too little, and the degree of inhibition of gangue ore is not enough and too much, and it is easy to interfere with the target mineral, but led to gangue mineral into phosphorus concentrate, affecting the quality of phosphorus concentrate products. Carboxymethylcellulose is a polymer inhibitor, and can produce flocculation to fine minerals. When the amount is too large, it will interfere with the separation of phosphate minerals, reduce the phosphorus grade, and recovery of phosphorus concentrate products [30]. It is reasonable to use 400 g/t carboxymethylcellulose, and a phosphorous concentrate with a P 2 O 5 of 22.53% and P 2 O 5 recovery of 72.51% can be obtained.  Figure 5 show that the appropriate addition of carboxymethylcellulose as an inhibitor can improve the effect of phosphorus flotation; too little, and the degree of inhibition of gangue ore is not enough and too much, and it is easy to interfere with the target mineral, but led to gangue mineral into phosphorus concentrate, affecting the quality of phosphorus concentrate products. Carboxymethylcellulose is a polymer inhibitor, and can produce flocculation to fine minerals. When the amount is too large, it will interfere with the separation of phosphate minerals, reduce the phosphorus grade, and recovery of phosphorus concentrate products [30]. It is reasonable to use 400 g/t carboxymethylcellulose, and a phosphorous concentrate with a P2O5 of 22.53% and P2O5 recovery of 72.51% can be obtained.

Effect of Grinding Fineness
Apatite and fine-grained gangue minerals are inset and symbiosis in the form of mechanical mixing. It is necessary to achieve high grinding fineness to realize monomer dissociation of most gangue minerals such as collophosphate and quartz. However, if grinding fineness is too high, overgrinding will occur, and the sorting effect will be reduced.  Figure 6 show that with the increase of grinding fineness, P2O5 grade of phosphorus concentrate changed regularly. When < 0.038 mm occupying 90%, the maximum value of P2O5 grade is 25.63%. The P2O5 grade of concentrate begins to decline with grinding fineness increasing. The principle is that with the increase of grinding fineness, the dissociation degree of mineral monomer increases continuously, but when the grinding fineness is too high, it will result in over-grinding phenomenon, gangue minerals float up in large quantities, causing the grade of concentrate to drop.

Effect of Grinding Fineness
Apatite and fine-grained gangue minerals are inset and symbiosis in the form of mechanical mixing. It is necessary to achieve high grinding fineness to realize monomer dissociation of most gangue minerals such as collophosphate and quartz. However, if grinding fineness is too high, over-grinding will occur, and the sorting effect will be reduced.
Results in Figure 6 show that with the increase of grinding fineness, P 2 O 5 grade of phosphorus concentrate changed regularly. When < 0.038 mm occupying 90%, the maximum value of P 2 O 5 grade is 25.63%. The P 2 O 5 grade of concentrate begins to decline with grinding fineness increasing. The principle is that with the increase of grinding fineness, the dissociation degree of mineral monomer increases continuously, but when the grinding fineness is too high, it will result in over-grinding phenomenon, gangue minerals float up in large quantities, causing the grade of concentrate to drop. After comprehensive consideration of the concentrate grade and recovery, grinding fineness < 0.039 mm occupying 90% of phosphorous flotation, and phosphorous concentrate with a P 2 O 5 grade of 25.63% and P 2 O 5 recovery of 70.26% can be obtained.

Effect of Grinding Fineness
Apatite and fine-grained gangue minerals are inset and symbiosis in the form of mechanical mixing. It is necessary to achieve high grinding fineness to realize monomer dissociation of most gangue minerals such as collophosphate and quartz. However, if grinding fineness is too high, overgrinding will occur, and the sorting effect will be reduced.  Figure 6 show that with the increase of grinding fineness, P2O5 grade of phosphorus concentrate changed regularly. When < 0.038 mm occupying 90%, the maximum value of P2O5 grade is 25.63%. The P2O5 grade of concentrate begins to decline with grinding fineness increasing. The principle is that with the increase of grinding fineness, the dissociation degree of mineral monomer increases continuously, but when the grinding fineness is too high, it will result in over-grinding phenomenon, gangue minerals float up in large quantities, causing the grade of concentrate to drop. After comprehensive consideration of the concentrate grade and recovery, grinding fineness < 0.039 18

Effect of Pulp pH
The effect of different flotation pH values on phosphorus flotation separation is shown in Figure 7. In the process of flotation, the pH value of the pulp has a great influence on the physical and chemical properties of the mineral surface, especially whether the flotation agents can produce a certain physical or chemical adsorption on the mineral, so as to achieve the wettability change between the target mineral and non-target mineral [31]. Increasing the pH value of flotation pulp is beneficial to raising P 2 O 5 grade of phosphorus concentrate. When the pH value exceeds 9, P 2 O 5 grade and recovery of phosphorus concentrate begin to decrease, indicating that slurry flotation at pH = 9 is conducive to the separation of phosphate minerals. The P 2 O 5 grade and P 2 O 5 recovery of phosphorus concentrate were 28.33% and 73.64%, respectively.

Effect of Pulp pH
The effect of different flotation pH values on phosphorus flotation separation is shown in Figure  7. In the process of flotation, the pH value of the pulp has a great influence on the physical and chemical properties of the mineral surface, especially whether the flotation agents can produce a certain physical or chemical adsorption on the mineral, so as to achieve the wettability change between the target mineral and non-target mineral [31]. Increasing the pH value of flotation pulp is beneficial to raising P2O5 grade of phosphorus concentrate. When the pH value exceeds 9, P2O5 grade and recovery of phosphorus concentrate begin to decrease, indicating that slurry flotation at pH = 9 is conducive to the separation of phosphate minerals. The P2O5 grade and P2O5 recovery of phosphorus concentrate were 28.33% and 73.64%, respectively.

Effect of Flotation Concentration
The concentration of flotation has a great influence on the physicochemical adsorption of flotation agents and minerals. As the concentration increases, the slurry viscosity increases, and the mechanical resistance between minerals increases, the adhesion between minerals and bubbles are affected, and the target minerals are easily separated from bubbles and the separation indexes are affected. On the contrary, if the concentration decreases, the concentration of flotation agents will decrease, resulting in an increase in the consumption of agents [32]. Under the premise of the same drug dose, if the concentration is too low, it will have a certain impact on the concentrate recovery.
It can be seen from Figure 8 that when the flotation concentration was 20%-30%, the P2O5 grade of phosphorus concentrate decreased from 28.66% to 28.29%, and the P2O5 recovery increased from 63.75% to 74.87%. When the flotation concentration was 35%-45%, the P2O5 grade of phosphorus concentrate decreased from 25.11% to 17.56%, and the P2O5 recovery rate increased from 75.12% to 76.89%. This indicates that the concentration of flotation pulp is 30%, and the P2O5 grade and recovery rate of the obtained phosphorus concentrate are 28.29% and 73.64%, respectively.

Effect of Flotation Concentration
The concentration of flotation has a great influence on the physicochemical adsorption of flotation agents and minerals. As the concentration increases, the slurry viscosity increases, and the mechanical resistance between minerals increases, the adhesion between minerals and bubbles are affected, and the target minerals are easily separated from bubbles and the separation indexes are affected. On the contrary, if the concentration decreases, the concentration of flotation agents will decrease, resulting in an increase in the consumption of agents [32]. Under the premise of the same drug dose, if the concentration is too low, it will have a certain impact on the concentrate recovery.
It can be seen from Figure 8 that when the flotation concentration was 20-30%, the P 2 O 5 grade of phosphorus concentrate decreased from 28.66% to 28.29%, and the P 2 O 5 recovery increased from 63.75% to 74.87%. When the flotation concentration was 35-45%, the P 2 O 5 grade of phosphorus concentrate decreased from 25.11% to 17.56%, and the P 2 O 5 recovery rate increased from 75.12% to 76.89%. This indicates that the concentration of flotation pulp is 30%, and the P 2 O 5 grade and recovery rate of the obtained phosphorus concentrate are 28.29% and 73.64%, respectively.

Effect of Different pH Regulators
The effect of different flotation pH regulators on phosphorus flotation separation is shown in Figure 9. The effect of sodium hydroxide and lime as pH regulator of flotation is obviously worse than that of sodium carbonate and sodium hydroxide. When sodium carbonate was used as a pH regulator, phosphorus concentrate with P2O5 grade of 28.69% and P2O5 recovery of 76.02% was produced. When sodium hydroxide was used as a pH regulator, phosphorus concentrate with P2O5 grade of 28.29% and P2O5 recovery of 74.87% was obtained. The reasons for this phenomenon are with amine cationic collector gangue mineral separation of phosphate rock minerals and effect is poorer, and Ca 2+ , Mg 2+ , Ca(OH) + , and Mg(OH) + in the solution later living fossil of the flotation of gangue, such as lower mineral separation, so the fatty acid collector (oxidized paraffin soap) sorted, Na2CO3 as pH adjusting agent, CO3 2-in the solution, and HCO3 − and Ca 2+ on the surface of the quartz. Ca 2+ , Mg 2+ , Ca(OH) + , and Mg(OH) + created CaCO3 and MgCO3, and then from the gangue mineral surface and the purpose of separation will be achieved [33][34][35].

Effect of Stage on Flotation Scavenging Process
Phosphorus concentrate with P2O5 grade of 28.69% and P2O5 recovery of 76.02% was obtained by one rough flotation process from the low-grade phosphorus-bearing V-Ti magnetite tailings. In order to further upgrade the phosphorus comprehensive recovery, scavenging time tests were carried out to investigate on P2O5 grade and recovery of froth products. The flotation scavenging process was shown in Figure 10, and the test results were shown in Table 3.

Effect of Different pH Regulators
The effect of different flotation pH regulators on phosphorus flotation separation is shown in Figure 9. The effect of sodium hydroxide and lime as pH regulator of flotation is obviously worse than that of sodium carbonate and sodium hydroxide. When sodium carbonate was used as a pH regulator, phosphorus concentrate with P 2 O 5 grade of 28.69% and P 2 O 5 recovery of 76.02% was produced. When sodium hydroxide was used as a pH regulator, phosphorus concentrate with P 2 O 5 grade of 28.29% and P 2 O 5 recovery of 74.87% was obtained. The reasons for this phenomenon are with amine cationic collector gangue mineral separation of phosphate rock minerals and effect is poorer, and Ca 2+ , Mg 2+ , Ca(OH) + , and Mg(OH) + in the solution later living fossil of the flotation of gangue, such as lower mineral separation, so the fatty acid collector (oxidized paraffin soap) sorted, Na 2 CO 3 as pH adjusting agent, CO 3 2− in the solution, and HCO 3 − and Ca 2+ on the surface of the quartz. Ca 2+ , Mg 2+ , Ca(OH) + , and Mg(OH) + created CaCO 3 and MgCO 3 , and then from the gangue mineral surface and the purpose of separation will be achieved [33][34][35].

Effect of Different pH Regulators
The effect of different flotation pH regulators on phosphorus flotation separation is shown in Figure 9. The effect of sodium hydroxide and lime as pH regulator of flotation is obviously worse than that of sodium carbonate and sodium hydroxide. When sodium carbonate was used as a pH regulator, phosphorus concentrate with P2O5 grade of 28.69% and P2O5 recovery of 76.02% was produced. When sodium hydroxide was used as a pH regulator, phosphorus concentrate with P2O5 grade of 28.29% and P2O5 recovery of 74.87% was obtained. The reasons for this phenomenon are with amine cationic collector gangue mineral separation of phosphate rock minerals and effect is poorer, and Ca 2+ , Mg 2+ , Ca(OH) + , and Mg(OH) + in the solution later living fossil of the flotation of gangue, such as lower mineral separation, so the fatty acid collector (oxidized paraffin soap) sorted, Na2CO3 as pH adjusting agent, CO3 2-in the solution, and HCO3 − and Ca 2+ on the surface of the quartz. Ca 2+ , Mg 2+ , Ca(OH) + , and Mg(OH) + created CaCO3 and MgCO3, and then from the gangue mineral surface and the purpose of separation will be achieved [33][34][35].

Effect of Stage on Flotation Scavenging Process
Phosphorus concentrate with P2O5 grade of 28.69% and P2O5 recovery of 76.02% was obtained by one rough flotation process from the low-grade phosphorus-bearing V-Ti magnetite tailings. In order to further upgrade the phosphorus comprehensive recovery, scavenging time tests were carried out to investigate on P2O5 grade and recovery of froth products. The flotation scavenging process was shown in Figure 10, and the test results were shown in Table 3.

Effect of Stage on Flotation Scavenging Process
Phosphorus concentrate with P 2 O 5 grade of 28.69% and P 2 O 5 recovery of 76.02% was obtained by one rough flotation process from the low-grade phosphorus-bearing V-Ti magnetite tailings. In order to further upgrade the phosphorus comprehensive recovery, scavenging time tests were carried out to investigate on P 2 O 5 grade and recovery of froth products. The flotation scavenging process was shown in Figure 10, and the test results were shown in Table 3. occurrence of phosphorous in tailings. Increasing the number of scavenging is mainly reflected in increasing the number of flotation machine slots in production, thus increasing the investment of preequipment. However, considering the high economic value of phosphorous, although increasing scavenging time will lead to decreasing P2O5 grade of phosphorous concentrate, from the perspective of comprehensive utilization of resources, it is still reasonable to obtain rough phosphorous concentrate by the direction flotation process of one roughing and three scavenging.

Effect of Stage on Flotation Cleaning Process
Through the effect experiment of flotation scavenging on P2O5 grade and recovery, with the flotation process of one roughing and three scavenging, phosphorus rough concentrate with a P2O5 grade of 23.12% and P2O5 recovery of 94.07% was obtained. According to the quality standard of phosphorous concentrate with the grade of P2O5 ≥ 28%). Therefore, the phosphorus rough concentrate Scavenging Ⅱ

P-bearing V-Ti magnetite tailings
Grinding fineness ＜0.038 mm occupying 90% × pH=9 (adjusting by sodium carbonate) ,3min × Carboxymethyl cellulose 400 g/t, 3 min × Oxidized paraffin wax soap 300 g/t, 3 min Roughing × pH=9 (adjusting by sodium carbonate) ,3min × Carboxymethyl cellulose 200 g/t, 3 min × Oxidized paraffin wax soap 150 g/t, 3 min ScavengingⅠ × pH=9 (adjusting by sodium carbonate) ,3min × Carboxymethyl cellulose 100 g/t, 3 min × Oxidized paraffin wax soap 75 g/t, 3 min × Pine oil 5 g/t, 3 min × pH=9 (adjusting by sodium carbonate) ,3min × Carboxymethyl cellulose 100 g/t, 3 min × Oxidized paraffin wax soap 75 g/t, 3 min × Pine oil 5 g/t, 3 min Scavenging Ⅲ FrothⅠ FrothⅡ Froth Ⅲ Froth Ⅳ Tailings  The direction flotation process of phosphorous-bearing V-Ti magnetite tailings after one roughing and three scavengings can obtain the separation index of phosphorous concentrate, with a P 2 O 5 grade of 23.12% and P 2 O 5 recovery of 94.07%. Compared with the primary roughing, the grade of cobalt decreased by (28.69 − 23.12)% = 5.57 percentage points, and the recovery of P 2 O 5 increased by (94.07 − 75.83)% = 18.24 percentage points. The index increased slightly, which was related to the occurrence of phosphorous in tailings. Increasing the number of scavenging is mainly reflected in increasing the number of flotation machine slots in production, thus increasing the investment of pre-equipment. However, considering the high economic value of phosphorous, although increasing scavenging time will lead to decreasing P 2 O 5 grade of phosphorous concentrate, from the perspective of comprehensive utilization of resources, it is still reasonable to obtain rough phosphorous concentrate by the direction flotation process of one roughing and three scavenging.

Effect of Stage on Flotation Cleaning Process
Through the effect experiment of flotation scavenging on P 2 O 5 grade and recovery, with the flotation process of one roughing and three scavenging, phosphorus rough concentrate with a P 2 O 5 grade of 23.12% and P 2 O 5 recovery of 94.07% was obtained. According to the quality standard of phosphorous concentrate with the grade of P 2 O 5 ≥ 28%). Therefore, the phosphorus rough concentrate should be further processed by cleaning to improve the P 2 O 5 grade. The technological process is shown in Figure 11, and the results are shown in Table 4 Results in Table 4 show that the improvement of P2O5 grade is obviously with the increase of concentrating times. Through the direction flotation process of one roughing, three scavenging, and four concentrating, the highest phosphorus separation indexes can be obtained from the low-grade P-containing vanadium titano-magnetite tailings: P2O5 grade of 32.11% and P2O5 recovery of 79.99%. Compared with the indexes of phosphorous rough concentrate before concentration, the P2O5 grade increased by (32.11 − 23.14) % = 8.97% and cobalt recovery rate decreased by (94.07 − 80.00% × 94.07) % = 18.81%. Therefore, an optimized phosphorous concentrate with P2O5 grade of 29.77% and P2O5 recovery of 90.57% can be produced using a three-stage concentration process.

The Whole Flotation Flowsheet Test of Recovering Phosphorous
Combined with the technological mineralogical characteristics of phosphorous in the P-bearing V-Ti magnetite tailings, technological conditions test, scavenging, and concentrating test results, the separation process of phosphorous is optimized and the closed-circuit flotation process of one roughing, three scavenging, and three concentrating is adopted. The gangue minerals are further inhibited by increasing the amount of CMC in the concentrating process to ensure that the P2O5 grade of the phosphorous concentrate is increased to more than 30% and the test indexes of the whole process flow are also examined. The flotation process (shown as Figure 12) was used to carry out the whole process test. The results are shown in Table 5. Cleaning Ⅲ Cleaning Ⅳ

Middlings Ⅱ
Middlings Ⅲ Middlings Ⅳ Figure 11. Time on flotation cleaning flowsheet. Results in Table 4 show that the improvement of P 2 O 5 grade is obviously with the increase of concentrating times. Through the direction flotation process of one roughing, three scavenging, and four concentrating, the highest phosphorus separation indexes can be obtained from the low-grade P-containing vanadium titano-magnetite tailings: P 2 O 5 grade of 32.11% and P 2 O 5 recovery of 79.99%. Compared with the indexes of phosphorous rough concentrate before concentration, the P 2 O 5 grade increased by (32.11 − 23.14) % = 8.97% and cobalt recovery rate decreased by (94.07 − 80.00% × 94.07) % = 18.81%. Therefore, an optimized phosphorous concentrate with P 2 O 5 grade of 29.77% and P 2 O 5 recovery of 90.57% can be produced using a three-stage concentration process.

The Whole Flotation Flowsheet Test of Recovering Phosphorous
Combined with the technological mineralogical characteristics of phosphorous in the P-bearing V-Ti magnetite tailings, technological conditions test, scavenging, and concentrating test results, the separation process of phosphorous is optimized and the closed-circuit flotation process of one roughing, three scavenging, and three concentrating is adopted. The gangue minerals are further inhibited by increasing the amount of CMC in the concentrating process to ensure that the P 2 O 5 grade of the phosphorous concentrate is increased to more than 30% and the test indexes of the whole process flow are also examined. The flotation process (shown as Figure 12) was used to carry out the whole process test. The results are shown in Table 5. This study adopted the direction flotation process of one roughing, three scavengings, and three cleanings to recover phosphorous from the low-grade P-bearing V-Ti magnetite tailings, obtaining the phosphorous concentrate with a P2O5 grade of 31.35% and P2O5 recovery of 88.02%, which were superior to the single-condition test results, and further showed that the flotation process had good repeatability.

Cleaning Ⅱ
Cleaning Ⅲ × CMC 100 g/t × CMC 50 g/t × CMC 25 g/t   This study adopted the direction flotation process of one roughing, three scavengings, and three cleanings to recover phosphorous from the low-grade P-bearing V-Ti magnetite tailings, obtaining the phosphorous concentrate with a P 2 O 5 grade of 31.35% and P 2 O 5 recovery of 88.02%, which were superior to the single-condition test results, and further showed that the flotation process had good repeatability.

Analysis and Characterization of Phosphous Concentrate
Low grade P-Containing vanadium titano-magnetite tailings from iron and titanium separation in the Miyi Region were treated using a direction flotation process. The separation indexes of phosphorous concentrate with a P 2 O 5 grade of 31.25% and P 2 O 5 recovery of 87.94% were obtained, realizing the recovery of valuable element phosphorous. The main chemical composition of phosphorous concentrate was analyzed by XRF smear quantitative analysis method, and the results are shown in Table 6. The main mineral of phosphorous concentrate was analyzed and characterized by X-ray diffraction and scanning electron microscope-energy disperse spectroscopy (SEM-EDS). The analysis and characterization of XRD and SEM-EDS results were shown in Figures 13 and 14 respectively. phosphorous concentrate was analyzed by XRF smear quantitative analysis method, and the results are shown in Table 6. The main mineral of phosphorous concentrate was analyzed and characterized by X-ray diffraction and scanning electron microscope-energy disperse spectroscopy (SEM-EDS). The analysis and characterization of XRD and SEM-EDS results were shown in Figures 13 and 14 respectively.     Analysis and characterization results from Table 6 and Figures 13 and 14 show that direction flotation process of one roughing, three scavengings, and three cleanings was suitable for recovering phosphorous from the low-grade P-bearing Vi-Ti magnetite tailings. Most gangue minerals enter the flotation tailings, and a phosphorus concentrate with P 2 O 5 grade of 31.25% was obtained. Compared with the P-bearing vanadium titano-magnetite, gangue minerals such as olivine, hornblende, feldspar, chlorite, mica, quartz, dolomite, and calcite decrease obviously after flotation. The main minerals in phosphorous concentrate are apatite, olivine, and feldspar.

Conclusions
Based on the direct flotation results of extracting phosphorous obtained in this study, we drew the main following conclusions: (1) The low-grade P-bearing V-Ti magnetite tailings sample was collected from a V-Ti magnetite dressing plant by magnetic separation and flotation in the Miyi area of China, and the P-bearing V-Ti magnetite tailings contained P 2 O 5 of 1.42%. Apatite was the main valuable mineral; gangue minerals were mica, chlorite, feldspar, calcite, etc. (2) The effect of different flotation conditions on phosphorus separation shows that using oxidized paraffin soap as flotation collector of phosphate minerals and carboxymethylcellulose as gangue mineral inhibitor can effectively recover the valuable element phosphorus in vanadium-titanium magnetite tailings. Phosphorous concentrate with a P 2 O 5 grade of 31.35% and P 2 O 5 recovery of 88.02% was obtained by a direction flotation process of one roughing, three scavengings, and three cleanings from the P-bearing V-Ti magnetite tailings. The extraction of phosphorus is remarkable, and the efficient utilization of phosphorous of low-grade phosphorous-bearing V-Ti tailings in the Miyi region of China can be realized finally. (3) Studies of the characterization and analysis of phosphorous concentrate by XRD, SEM, and EDS indicated that the main minerals in phosphorous concentrate are apatite, olivine, and feldspar. It also further shows that carboxymethylcellulose, as an inhibitor of gangue ore, can significantly reduce the gangue mineral content in phosphorus concentrate, such as most gangue minerals olivine, hornblende, feldspar, chlorite, mica, quartz, dolomite, and calcite enter into flotation tailings. In addition, hornblende, as one of the main scandium bearing minerals in vanadium-titanium magnetite tailings, enters into flotation tailings, creating favorable conditions for the next step of scandium separation and extraction.