Biological reduction method and system for removing iron from silica sand

Abstract

The present invention relates to iron removal from silica sand, and specifically to a biological reduction method and system for iron removal from silica sand. By using Shewanella sp. bacteria to reduce crystalline iron, and simultaneously improving the iron removal rate through the synergistic effect of sodium lactate, sulfur-containing compounds and electron mediators, and accelerating the iron removal speed by washing with organic acids. Compared with the existing methods, the biological reduction method for iron removal from silica sand of the present invention can not only effectively remove crystalline iron in silica sand, but also recycle Shewanella sp. bacterial liquid and organic acid solution.

Description

Technical Field

[0001] The present invention relates to iron removal from silica sand, and specifically to a biological reduction method and system for iron removal from silica sand. Background Art

[0002] Silica sand, also known as quartz sand or silicon dioxide, is an important raw material for manufacturing ordinary glass, quartz glass, water glass, optical fibers, electronic components, optical instruments, refractory materials, etc. Currently, most of the silica sand particles commonly used in industry are obtained from natural silica sand ores through processes such as crushing, sand making, and sand washing, and they usually contain iron impurities. The iron content in silica sand ranges from approximately 600 to 900 ppm (calculated as Fe2O3). Different purities of quartz sand have strict measurement standards for their iron content. Therefore, it is necessary to reduce the iron impurity content in silica sand to meet specific usage standards. Commonly used methods for iron removal from silica sand include water washing, ultrasonic treatment, magnetic separation, and acid leaching. In practical applications, silica sand is first pretreated by physical methods such as water washing, scrubbing, magnetic separation, and ultrasonic waves to remove most of the iron impurities; then, chemical methods such as acid leaching or complexation methods are used to further reduce the iron impurity content to meet specific application standards. The acid leaching method is the most commonly used chemical iron removal method in industry. The iron impurities in silica minerals are mainly trivalent iron (Fe(III)) minerals, and usually strong acids (such as H2SO4, HCl, and HNO3, etc.) are required to dissolve them. At the same time, the assistance of HF is also needed to remove the iron impurities in the SiO2 lattice to meet specific usage standards. However, the acid leaching method will produce a large amount of fluorine-containing acidic wastewater, with a high sewage treatment cost and may also cause environmental pollution.

[0003] The biological iron removal method for silica sand has characteristics such as low energy consumption and environmental friendliness, and mainly includes two strategies: microbial leaching and microbial reduction. Microbial leaching is to use the metabolites produced by microorganisms (such as Aspergillus niger, Acidithiobacillus ferrooxidans), such as organic acids, amino acids, etc., to leach and remove iron from quartz sand. Biological iron reduction is to use iron-reducing bacteria (such as Klebsiella oxytoca, Thermoanaerobacter ethanolicus, iron-reducing bacterium RBEL3, iron-reducing bacterium FL-H1, iron-reducing bacterium FeRB-FL1401) to reduce insoluble trivalent iron to divalent iron with higher solubility. However, the microbial leaching method has a long leaching time and low efficiency for crystalline Fe(III) compounds (such as Fe2O3). The Fe2O3 mineral is non-conductive, and the reduction degree of general iron-reducing bacteria for crystalline Fe2O3 in silica sand is limited. Summary of the Invention

[0004] Based on this, the present invention provides a biological reduction method and system for iron removal from silica sand, which solves at least one problem in the prior art.

[0005] In a first aspect, the present invention provides a biological reduction method for iron removal from silica sand, which includes the following steps:

[0006] Mix the iron-containing silica sand with Shewanella sp. bacterial solution, add sodium lactate, sulfur-containing compound and electron mediator to obtain a mixed solution, maintain the pH of the mixed solution at 6 - 7.5, and place it in an anaerobic environment for 2 - 10 days;

[0007] Separate the solid substance from the mixed solution to obtain reduced iron-containing silica sand;

[0008] Wash the reduced iron-containing silica sand with an organic acid solution at 20 - 100 °C.

[0009] In a second aspect, the present invention provides a biological reduction iron removal system for silica sand, which includes:

[0010] A biological reduction pool for accommodating a mixed solution of iron-containing silica sand, Shewanella sp. bacterial solution, sodium lactate, sulfur-containing compound and electron mediator;

[0011] A sedimentation pool for sedimenting the solid substance in the mixed solution to obtain reduced iron-containing silica sand;

[0012] An acid washing pool for accommodating the reduced iron-containing silica sand and organic acid.

[0013] Due to the adoption of the above technical solutions, the embodiments of the present invention have at least the following beneficial effects:

[0014] (1) Use iron-reducing bacteria with extracellular electron transfer (i.e., electroactive iron-reducing bacteria) Shewanella sp. to reduce the Fe2O3 mineral in silica sand, and improve the reduction degree of crystalline Fe2O3 in silica sand by strengthening the electron transfer of electroactive iron-reducing bacteria and regulating divalent iron products. The reduction rate of iron is close to 85%;

[0015] (2) Use organic acid to wash the reduced iron-containing silica sand after bacterial reduction, which can improve the iron removal efficiency of silica sand, and the iron removal rate exceeds 85%; Shewanella sp.

[0016]

[0016] (3) Can improve the whiteness of silica sand, and the whiteness of silica sand can reach 95%;

[0017] (4) Shewanella sp. The bacterial solution, sulfur element and organic acid solution can all be reused, which is green and environmentally friendly. Description of the Drawings

[0018] Figure 1 For Shewanella sp. SEM morphology and growth curve of bacteria.

[0019] Figure 2This is a dot line graph showing the change of Fe(III) reduction rate over time when adding 2.5 mmol / L Na2S2O3 and 5 mmol / L Na2S·9H2O in the embodiments of the present invention.

[0020] Figure 3 This is a dot line graph showing the change of Fe(III) reduction rate over time when the concentrations of Na2S2O3 are 2.5, 2.0, 1.5, 1.0, and 0.5 mmol / L respectively in the embodiments of the present invention.

[0021] Figure 4 This is the reduction effect diagram of the Fe2O3 suspension when the pH values are 3.0, 4.0, and 5.0 in the embodiments of the present invention.

[0022] Figure 5 This is a dot line graph showing the change of Fe(III) reduction rate over time when the pH values are 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, and 9.0 in the embodiments of the present invention.

[0023] Figure 6 This is a dot line graph showing the change of pH value over time when the Fe2O3 biological reduction system is uncompensated and the pH compensation value is 6.50 every 24 h in the embodiments of the present invention

[0024] Figure 7 This is a bar graph showing the change of Fe(III) reduction rate over time when the uncompensated pH and the pH compensation value are 6.50 every 24 h in the embodiments of the present invention.

[0025] Figure 8 This is a dot line graph showing the change of Fe(III) reduction rate over time when adding 5, 10, 50, 100, and 500 mg / L HA in the embodiments of the present invention.

[0026] Figure 9 This is a dot line graph showing the change of Fe(III) reduction rate over time when adding 0.1, 1.0, 5.0, and 10.0 mmol / L AQDS in the embodiments of the present invention.

[0027] Figure 10 This is a color change diagram of 500 g of iron-containing silica sand before and after 3 d and 7 d of biological reduction in the embodiments of the present invention.

[0028] Figure 11 This is a dot line graph showing the change of the total Fe value in silica sand when the concentrations of H2C2O4 are 120, 100, 80, 60, 40, 20, and 0 mmol / L in the embodiments of the present invention.

[0029] Figure 12 This is a dot line graph showing the change of the total Fe value in silica sand when the pickling temperatures are 100, 80, 60, 40, and 20 °C in the embodiments of the present invention.

[0030] Figure 13 This is the color change diagram of 20 g of silica sand before and 7 days after biological reduction using biological reduction wastewater (supernatant) in the embodiments of the present invention.

[0031] Figure 14 This is the bar graph of the change in COD value of silica sand soaked in 100 mmol / L H2C2O4 with the number of cycles in the embodiments of the present invention.

[0032] Figure 15 This is the color change diagram of 0.8 mmol / L Fe(OH)3 before biological reduction (a. without adding sulfide-containing substances, b. adding 2.5 mmol / L Na2S2O3) and after 4 h, 3 d, and 7 d in the embodiments of the present invention.

[0033] Figure 16 This is the color change diagram of 0.8 mmol / L Fe2O3 before biological reduction (without adding sulfide-containing substances) and after 7 d in the embodiments of the present invention.

[0034] Figure 17 This is the color change diagram of 10 g of iron-containing silica sand before biological reduction (without adding sulfide-containing substances) and after 7 d in the embodiments of the present invention.

[0035] Figure 18 This is the X-ray diffraction pattern diagram of Fe(OH)3 and Fe2O3 in the embodiments of the present invention.

[0036] Figure 19 This is the Raman spectrum diagram of iron-containing silica sand and α-Fe2O3 in the embodiments of the present invention.

[0037] Figure 20 This is the schematic diagram of the biological reduction of iron-containing silica sand and the process of removing iron by pickling organic matter in the embodiments of the present invention. Detailed implementation manners

[0038] The following will clearly and completely describe the concept of the present invention and the resulting technical effects to fully elaborate the purpose, solution, and effects of the present invention.

[0039] In order to improve the reduction degree of crystalline Fe2O3 in silica sand, enhance the iron removal efficiency and whiteness of silica sand, and at the same time reduce pollutant emissions to achieve green iron removal of silica sand, the present invention provides a method and system for biological reduction of iron removal from silica sand.

[0040] In the first aspect, the method for biological reduction of iron removal from silica sand includes the following steps:

[0041] Put the iron-containing silica sand and Shewanella sp.Mix the bacterial solution, add sodium lactate, sulfur-containing compounds and electron mediators to obtain a mixed solution, maintain the pH of the mixed solution at 6-7.5, and place it in an anaerobic environment for 2-10 days;

[0042] Separate the solid matter from the mixed solution to obtain reduced iron-containing silica sand;

[0043] Wash the reduced iron-containing silica sand with an organic acid solution at 20-100 °C.

[0044] The iron-containing silica sand may contain crystalline iron compounds, such as crystalline Fe2O3. The method for removing iron from bioreduced silica sand utilizes Shewanella sp. bacteria to reduce crystalline iron, and at the same time improve the iron removal rate through the synergistic effect of sodium lactate, sulfur-containing compounds and electron mediators, and accelerate the iron removal speed through organic acid washing. Compared with the existing methods, this method can not only effectively remove crystalline iron in silica sand, but also recycle Shewanella sp. the bacterial solution and the organic acid solution.

[0045] In some alternative embodiments, the Shewanella sp. OD600 value of the bacterial solution is 0.6-0.8. Within this OD600 value range, Shewanella sp. the bacteria grow vigorously, which is beneficial to iron removal.

[0046] In some alternative embodiments, the concentration of sodium lactate in the mixed solution is 0.1-1 mol / L.

[0047] In some alternative embodiments, the sulfur-containing compound is one or more of Na2S, Na2S2O3, elemental S, Na2SO3 and Na2SO4. The sulfur-containing compound combines with reduced divalent iron to form ferrous sulfide compounds, which enhances the reduction rate and efficiency of Fe2O3. Preferably, the sulfur-containing compound is Na2S or elemental S.

[0048] In some alternative embodiments, the concentration of the sulfur-containing compound in the mixed solution is 0.5-2.5 mmol / L (calculated as S element). Preferably, the concentration of the sulfur-containing compound in the mixed solution is 2-2.5 mmol / L.

[0049] In some alternative embodiments, the electron mediator is humic acid (HA) or sodium anthraquinone-2,6-disulfonate (AQDS). The redox active groups of humic acid and sodium anthraquinone-2,6-disulfonate are mainly quinone groups, which transfer electrons between respiratory chain protein complexes, thereby accelerating the iron removal speed. Preferably, the electron mediator is humic acid.

[0050] In some alternative embodiments, the concentration of the electron mediator in the mixed solution is 0.1 - 10 mmol / L. Preferably, the concentration of the electron mediator in the mixed solution is 5 mmol / L.

[0051] In some alternative embodiments, the organic acid solution is an aqueous oxalic acid solution.

[0052] In some alternative embodiments, the concentration of the organic acid solution is 20 - 120 mmol / L. Preferably, the concentration of the organic acid solution is 100 mmol / L.

[0053] In some alternative embodiments, the method for removing iron from bio-reduced silica sand further includes recovering the liquid substances in the mixed solution and repeating the steps for removing iron from silica sand. Preferably, after recovering the liquid substances in the mixed solution, sodium lactate and sulfur-containing compounds are supplemented (to restore their concentrations to the initial concentrations) and reused for removing iron from silica sand.

[0054] In some alternative embodiments, the method for removing iron from bio-reduced silica sand further includes recovering the organic acid solution and repeating the steps for removing iron from silica sand. Preferably, after recovering the organic acid, organic acid is supplemented (to restore the concentration of the organic acid to the initial concentration) and reused for removing iron from silica sand.

[0055] In a second aspect, the bio-reduced silica sand iron removal system includes:

[0056] A bio-reduction pool for containing a mixed solution of iron-containing silica sand, Shewanella sp. bacterial solution, sodium lactate, sulfur-containing compounds, and an electron mediator;

[0057] A sedimentation pool for sedimenting solid substances in the mixed solution to obtain reduced iron-containing silica sand;

[0058] An acid-washing pool for containing the reduced iron-containing silica sand and an organic acid.

[0059] In some alternative embodiments, a reflux pipeline is provided between the sedimentation pool and the bio-reduction pool to enable the liquid substances in the mixed solution to flow back to the bio-reduction pool.

[0060] In some alternative embodiments, a pump is provided on the reflux pipeline.

[0061] Some typical embodiments are introduced below.

[0062] In the following embodiments, Shewanella sp. bacteria ( MR-1Cultivate according to the following steps: Prepare an LB Broth solution (composed of tryptone, yeast extract, and NaCl) at a ratio of 25 g / L, and autoclave it at 121 °C for 25 min; after restoring to room temperature, inoculate in a laminar flow hood, inoculating 15 L at a time. Shewanella sp. Bacterial strain (strain number: CICC25104; original collection site: Oneida Lake, New York, USA), place it in a shaker at 35 °C (rotation speed: 300 r / min) and cultivate for 24 - 36 h; test the OD600 value of the bacterial liquid every 6 h, and when OD600 = 0.6 - 0.8, centrifuge the bacterial liquid and wash it three times with phosphate buffer solution to obtain enriched bacteria.

[0063] Take the bacteria that have grown vigorously in the LB Broth solution for about 24 h, fix the morphology of the bacteria with a small amount of 2.5% glutaraldehyde, and dehydrate them with ethanol at concentrations of 20%, 50%, 80%, and 100% respectively, and then Shewanella sp. perform SEM characterization. As Figure 1 shown, from the characterization results, it can be seen that MR-1 they are rod-shaped bacteria, including long rods and short rods. Moreover, with the extension of the culture time, Shewanella sp. the OD600 of the bacterial liquid increases, and after culturing for 30 hours Shewanella sp. the OD600 of the bacterial liquid begins to decrease.

[0064] In the following examples, the determination of the iron reduction rate (removal rate) is obtained by the ratio of the concentration of Fe(II) produced by biological reduction to the concentration of Fe(III) before reduction. The determination of the Fe(II) concentration uses the PPST colorimetric method, and 3-(2-pyridyl)-5,6-bis(4-benzenesulfonic acid)-1,2,4-triazene disodium (abbreviated as PPST) is used as the color reagent for Fe(II) to determine trace iron in water. In the range of pH = 2 - 9, in water, Ferrozine complexes with Fe 2+ to form a stable purple complex anion Fe(Ferroz)3 with good water solubility 4- , which has a maximum absorption peak at 562 nm. Its concentration can be accurately measured by a portable Lovibond spectrophotometer. The Lovibond spectrophotometer comes with a standard curve and can accurately measure the Fe(II) concentration within a certain range. If the total Fe in the solution is to be determined, hydroxylamine hydrochloride is used; Fe(III) in the solution is completely reduced to Fe(II), and then Fe(II) reacts with PPST for color development, and the total Fe ion concentration can be accurately measured.

[0065] Example 1: Use Shewanella sp. bacteria to reduce Fe2O3 in the presence of Na2S

[0066] Take 100 mL of 0.8 mmol / L Fe2O3 suspension (with an Fe content of 89.6 mg / L), add Na2S·9H2O until the Na2S content reaches 5 mmol / L, and add bacteria with OD600 = 0.6 - 0.8 (after centrifugation) and 2.5 mL of 0.175 mol / L C3H5O3Na solution. Adjust the pH value to 6.8 with 1 M dilute H2SO4 or saturated NaOH solution, and seal and place it in a 35 °C incubator for anaerobic reduction. Shewanella sp. bacteria (after centrifugation) and 2.5 mL of 0.175 mol / L C3H5O3Na solution. Adjust the pH value to 6.8 with 1 M dilute H2SO4 or saturated NaOH solution, and seal and place it in a 35 °C incubator for anaerobic reduction.

[0067] Example 2: Under the condition of Na2S2O3 participation, use Shewanella sp. bacteria to reduce Fe2O3

[0068] Take 100 mL of 0.8 mmol / L Fe2O3 suspension (with an Fe content of 89.6 mg / L), add Na2S2O3 until the Na2S2O3 content reaches 2.5 mmol / L, and add bacteria with OD600 = 0.6 - 0.8 (after centrifugation) and 2.5 mL of 0.175 mol / L C3H5O3Na solution. Adjust the pH value to 6.8 with 1 M dilute H2SO4 or saturated NaOH solution, and seal and place it in a 35 °C incubator for anaerobic reduction. Shewanella sp. bacteria (after centrifugation) and 2.5 mL of 0.175 mol / L C3H5O3Na solution. Adjust the pH value to 6.8 with 1 M dilute H2SO4 or saturated NaOH solution, and seal and place it in a 35 °C incubator for anaerobic reduction.

[0069] For Example 1 and Example 2, take 1 mL of the liquid every 24 h to measure its Fe(II) value, and determine the reduction efficiency of Fe(III) according to the concentration of Fe(II). The results are as Figure 2 shown. When adding 5 mmol / L Na2S·9H2O, the overall Fe(III) reduction rate increased by about 10% compared with 2.5 mmol / L Na2S2O3. The possible reason is that there is a competitive relationship between the FeS generated by reduction and the Fe3O4 that may be generated in the system.

[0070] Example 3: Under the condition of different concentrations of Na2S2O3 participation, use Shewanella sp. bacteria to reduce Fe2O3

[0071] Take five portions of 100 mL of 0.8 mmol / L Fe2O3 suspension (with an Fe content of 89.6 mg / L), and add Na2S2O3 until the Na2S2O3 content reaches 2.5, 2.0, 1.5, 1.0, 0.5 mmol / L respectively. Add bacteria with OD600 = 0.6 - 0.8 (after centrifugation) and 2.5 mL of 0.175 mol / L C3H5O3Na solution. Adjust the pH value to 6.5 with 1 M dilute H2SO4 or saturated NaOH solution, and seal and place it in a 35 °C incubator for anaerobic reduction. Shewanella sp. bacteria (after centrifugation) and 2.5 mL of 0.175 mol / L C3H5O3Na solution. Adjust the pH value to 6.5 with 1 M dilute H2SO4 or saturated NaOH solution, and seal and place it in a 35 °C incubator for anaerobic reduction.

[0072] As Figure 3 shown, the initial pH controlling the system reaction was 6.5. When adding 2.5 mmol / L Na2S2O3 and 2.0 mmol / L Na2S2O3, the final Fe(III) reduction rates were 58.40% and 63.99% respectively. When adding 1.0 mmol / L Na2S2O3 and 0.5 mmol / L Na2S2O3, the solution color started to turn black at 48 h of reduction, and the reduction rates were both lower than 20%. The main reason was that the concentration of Na2S2O3 was not enough to support the biological reduction of Fe2O3. When adding different concentrations of Na2S2O3, the average increase in the Fe(III) reduction rate at 10 d of reduction time compared to that at 5 d was about 1% - 2%. When controlling the concentration of Na2S2O3 at 2.0 mmol / L, the Fe(III) reduction rates were all about 64.02%, that is, the complete reduction time was only about 5 d. Therefore, when the addition concentration of Na2S2O3 was 2.0 mmol / L, it was beneficial to remove iron.

[0073] Example 4: Using Shewanella sp. bacteria to reduce Fe2O3

[0074] Take eight portions of 100 mL 0.8 mmol / L Fe2O3 suspension (Fe content was 89.6 mg / L), add Na2S2O3 to the content of Na2S2O3 reaching 2.0 mmol / L, and add bacteria with OD600 = 0.6 - 0.8 (after centrifugation) and 2.5 mL 0.175 mol / L C3H5O3Na solution. Adjust the pH value to 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0 with 1 M dilute H2SO4 or saturated NaOH solution, and seal and place in a 35 °C incubator for anaerobic reduction. Shewanella sp.

[0075] Figure 4 As Figure 5 shown, under acidic conditions (pH = 3.0, 4.0, 5.0) in the reaction system, the bacterial activity was poor and no reduction phenomenon occurred. Shewanella sp. It was shown that within the range of pH = 5.5 - 9.0, Fe2O3 could all undergo biological reduction reactions, indicating that bacteria were active within this pH range. As the pH value increased, especially under alkaline conditions, the Fe(III) reduction rate gradually decreased. When the initial pH value was 6.0 - 7.0, the biological reduction of Fe2O3 showed a relatively high reduction rate, and the Fe(III) reduction efficiency could reach about 62.87%, which also indicated that when the pH was 6.0 - 7.0 Shewanella sp.The activity of bacteria is high. The Fe(III) reduction rate at different initial pH values ​​at a reduction time of 10 days increased by an average of about 2% to 4% compared with the Fe(III) reduction rate at 5 days.

[0076] Example 5: Using under pH compensation conditions Shewanella sp. Bacterial reduction of Fe2O3

[0077] Take 100 mL of 0.8 mmol / L Fe2O3 suspension (containing 89.6 mg / L Fe), add Na2S2O3 until the Na2S2O3 content reaches 2.0 mmol / L, and add OD600 = 0.6 ~ 0.8 Shewanella sp. Bacteria (after centrifugation) and 2.5 mL 7 mol / L C3H5O3Na solution were added, and the pH value was adjusted to 6.87 with 1 M dilute H2SO4 or saturated NaOH solution, and the mixture was sealed and placed in a 35 ℃ constant temperature box for anaerobic reduction; the pH value was adjusted to 6.5 with 1 M dilute H2SO4 or saturated NaOH every 24 hours (pH compensation), and a control sample without pH adjustment was set up at the same time (no pH compensation was performed).

[0078] like Figure 6 and Figure 7 As shown in the figure, in the control case without adjusting the pH value, the pH value gradually increased from the initial 6.87 to 8.10 during the Fe2O3 bioreduction process. The reduction rate after pH compensation was generally higher than that before compensation. After pH compensation, the Fe(III) reduction rate reached 64.36% after 4 days, which was about 24 hours less than the reduction time before compensation.

[0079] Example 6: Using humic acid in the presence of Shewanella sp. Bacterial reduction of Fe2O3

[0080] Take five 100 mL portions of 0.8 mmol / L Fe2O3 suspension (containing 89.6 mg / L Fe), add Na2S2O3 to a Na2S2O3 content of 2.5 mmol / L, add humic acid (HA) to a HA concentration of 5, 10, 50, 100, and 500 mg / L, and add OD600 = 0.6 ~ 0.8 Shewanella sp. Bacteria (after centrifugation) and 2.5 mL 7 mol / L C3H5O3Na solution, adjust the pH to 6.8 with 1 M dilute H2SO4 or saturated NaOH solution, seal and place in a 35 ℃ constant temperature box for anaerobic reduction. At the same time, set up a blank control without adding HA (marked as blank in the figure, HA concentration is 0).

[0081] like Figure 8As shown, compared with the blank control group, the Fe(III) reduction rate with the addition of humic acid increased by 10% - 20% overall, and the highest reached 82.60%. The Fe(III) reduction rate with the addition of 10 mg / L HA was 83.71%, which was about 20% higher than that without the addition of electron mediators. When the HA concentration increased to 500 mg / L, the Fe(III) reduction rate decreased.

[0082] Example 7: Under the participation of sodium anthraquinone-2,6-disulfonate, use Shewanella sp. bacteria to reduce Fe2O3

[0083] Take four 100 mL 0.8 mmol / L Fe2O3 suspensions (with an Fe content of 89.6 mg / L), add Na2S2O3 to the Na2S2O3 content reaching 2.5 mmol / L, add sodium anthraquinone-2,6-disulfonate (AQDS) to the AQDS concentration of 0.1, 1.0, 5.0, 10.0 mmol / L, and add bacteria (after centrifugation) with OD600 = 0.6 - 0.8 Shewanella sp. and 2.5 mL of 7 mol / L C3H5O3Na solution, adjust the pH value to 6.8 with 1 M dilute H2SO4 or saturated NaOH solution, and seal and place it in a 35 °C incubator for anaerobic reduction. At the same time, set a blank control example without adding AQDS (marked as blank in the attached figure, AQDS concentration is 0).

[0084] As Figure 9 shown, the effect of adding different concentrations of AQDS to improve the Fe(III) reduction rate is not as significant as that of HA, and it is about 5% - 10% higher than that without adding AQDS. Among them, the Fe(III) reduction rate with 5.0 mmol / L AQDS was 75.89%. When the Fe2O3 biological reduction time was 10 d, the increase in the Fe(III) reduction rate compared with the reduction time of 5 d was about 1% - 2%.

[0085] The overall Fe(III) reduction rate with the addition of HA was about 8% - 10% higher than that with AQDS. The possible reason is that HA not only acts as an electron shuttle but also has a complexing effect on Fe2O3, promoting the transformation of crystalline Fe(III) into free Fe(III). As the concentration of free Fe(III) increases, the probability of chemical collisions in chemical reactions also increases, thus accelerating the biological reduction rate.

[0086] Example 8: Use Shewanella sp. bacteria to reduce iron-bearing silica sand

[0087] Take 500 g of dried silica sand, add deionized water until the liquid level completely covers the silica sand, add Na2S2O3 until the Na2S2O3 content reaches 90 mmol / L, and add 500 mL of bacteria with OD600 = 0.6 - 0.8 (after centrifugation) and 80 mL of 7 mol / L C3H5O3Na solution, and place them in an incubator at 35 °C for 7 days of biological reduction; filter out the supernatant of the completely biologically reduced silica sand, wash the silica sand several times with water and then divide it into six parts, and pickle them with 120, 100, 80, 60, 40, and 20 mmol / L H2C2O4 solution (pH = 3) respectively. Shewanella sp. After 7 days of biological reduction, as shown in , the color of the solution becomes significantly black. Take a water sample and test its Fe(II) to be 43 mg / L, that is, the Fe(III) reduction rate is 63.64%. Compare the iron content and whiteness of the silica sand pickled under the same conditions before reduction. The results show that the iron content of the pickled silica sand before reduction is 390 ppm; the iron content of the acid-treated silica sand after reduction is 170 ppm, and the whiteness is 95.6%.

[0088] such as Figure 10 After drying the pickled silica sand, add 8 mL of 12 mol / L HCl, react for more than 10 h and then add 92 mL of deionized water. Take 1 mL of the supernatant and test the total Fe value in the silica sand with a spectrophotometer. As shown in Figure 11 , after pickling with 100 mmol / L H2C2O4 (pH = 3), the total Fe value is about 240 ppm, and the whiteness and brightness also increase. This is because in addition to using its acidity, H2C2O4 may also have a complexing effect on Fe(III).

[0089] Example 9: Removal of iron from silica sand by washing and reducing with oxalic acid at different temperatures Figure 11 Take 500 g of dried silica sand, add deionized water until the liquid level completely covers the silica sand, add Na2S2O3 until the Na2S2O3 content reaches 90 mmol / L, and add 500 mL of bacteria with OD600 = 0.6 - 0.8 (after centrifugation) and 80 mL of 7 mol / L C3H5O3Na solution, and place them in an incubator at 35 °C for 7 days of biological reduction; filter out the supernatant of the completely biologically reduced silica sand, wash the silica sand several times with water and then divide it into five parts, and pickle them with 100 mmol / L H2C2O4 solution (pH = 3) at 100, 80, 60, 40, and 20 °C respectively.

[0090] such as

[0091] Take 500 g of dried silica sand, add deionized water until the liquid level completely covers the silica sand, add Na2S2O3 until the Na2S2O3 content reaches 90 mmol / L, and add 500 mL of bacteria with OD600 = 0.6 - 0.8 (after centrifugation) and 80 mL of 7 mol / L C3H5O3Na solution, and place them in an incubator at 35 °C for 7 days of biological reduction; filter out the supernatant of the completely biologically reduced silica sand, wash the silica sand several times with water and then divide it into five parts, and pickle them with 100 mmol / L H2C2O4 solution (pH = 3) at 100, 80, 60, 40, and 20 °C respectively. Shewanella sp. After 7 days of biological reduction, as shown in , the color of the solution becomes significantly black. Take a water sample and test its Fe(II) to be 43 mg / L, that is, the Fe(III) reduction rate is 63.64%. Compare the iron content and whiteness of the silica sand pickled under the same conditions before reduction. The results show that the iron content of the pickled silica sand before reduction is 390 ppm; the iron content of the acid-treated silica sand after reduction is 170 ppm, and the whiteness is 95.6%.

[0092] such as Figure 12As shown, the higher the pickling temperature, the less the total residual Fe in silica sand. In practical applications, adding a certain amount of H2C2O4 and appropriately increasing the temperature during pickling can achieve better washing effects.

[0093] Example 10: Reuse of silica sand biological reduction wastewater

[0094] Take two portions of 20 g of dried silica sand, add deionized water until the liquid level completely covers the silica sand, add Na2S2O3 until the Na2S2O3 content reaches 2.5 mmol / L, add 120 mL of bacteria with OD600 = 0.6 - 0.8 Shewanella sp. (after centrifugation) and 2.5 mL of 7 mol / L C3H5O3Na solution. One portion does not add HA, and the other portion adds 100 mg / L HA for comparison. Place them in an incubator at 35 °C for 7 days of biological reduction. Separate the upper mixed solution from the silica sand after 7 days of complete biological reduction, and centrifuge the upper mixed solution at 6000 r / min. Take another 20 g of iron-containing silica sand (i.e., dried silica sand without biological reduction), pour 80 mL of the centrifuged supernatant, and supplement Na2S2O3 to reach 1 mmol / L and 1 mL of 7 mol / L C3H5O3Na solution. After purging high-purity nitrogen for more than 20 min, place it in an incubator at 35 °C for anaerobic digestion. After complete biological reduction (7 days), take 1 mL of the water sample to test its Fe(II) value.

[0095] As Figure 10 shown, using the supernatant containing sulfide and nutrients to reduce iron-containing silica sand, it can be found that the solution color starts to turn black at the 3rd day of the reduction time and turns completely black until the 7th day of the reduction time. The Fe(III) reduction rate of the reactor with added HA is 54.49%, which is about 20% less than the reduction rate of silica sand without using biological reduction wastewater; similarly, the Fe(III) reduction rate of the reactor without added HA is about 23% less than the reduction rate of normal silica sand.

[0096] Example 11: Recycling oxalic acid for iron removal from silica sand

[0097] Take 500 g of dried silica sand, add deionized water until the liquid level completely covers the silica sand, add Na2S2O3 until the Na2S2O3 content reaches 90 mmol / L, add 500 mL of bacteria with OD600 = 0.6 - 0.8 Shewanella sp.Bacteria (after centrifugation) and 80 mL of 7 mol / L C3H5O3Na solution were placed in an incubator at 35 °C for 7 days of biological reduction. After complete biological reduction, the supernatant of the silica sand was filtered out and washed with water. The washed silica sand was divided into several portions, each portion being 50 g. 50 mL of 100 mM H2C2O4 was added to one portion of the washed silica sand and soaked; every 24 h, the upper layer of the H2C2O4 mixed solution was poured into a new 50 g portion of silica sand, and 2 mL of water sample was taken to test its COD value. As Figure 14 shown, the number of recycling times of 100 mmol / L H2C2O4 during the pickling process of silica sand was found. The concentration of 100 mmol / L H2C2O4 dropped to about half after 5 times of recycling.

[0098] Example 12: Continuous biological iron removal from silica sand

[0099] In an actual factory, a biological reduction pool and a pickling pool were configured to achieve continuous iron removal from silica sand. The process flow chart is as Figure 20 shown. To reduce 1 Kg of iron-containing silica sand (500 ppm Fe), 600 mL of electroactive Shewanella sp. bacterial solution was added; 150 mL of 7 mol / L carbon source (C3H5O3Na) was added; sulfur-containing compounds (0.2 mol / L Na2S2O3 or 0.4 mol / L Na2S) were added; 1 mmol / L of an electron shuttle with a quinone structure or 10 mg / L of humus was added. The pH was maintained at 6 in the sedimentation tank, and anaerobic reduction was carried out for 5 days. After the reduced silica sand was separated by solid-liquid separation, it was soaked and washed with 100 mmol / L oxalic acid solution at 70 °C and recycled.

[0100] Circulation of iron-containing biological reduction wastewater: Similar to Example 10, after the wastewater after solid-liquid separation was de-ironed, about 1 / 3 of the previously added nutrient content (150 mL of 7 mol / L C3H5O3Na) was supplemented and recycled for a new round of biological reduction of silica sand. The iron sulfide mixture after de-ironing the iron-containing wastewater could be dissolved by adding dilute sulfuric acid, and Fe(III) and sulfide were separated by adjusting its pH value, and the obtained sulfide was re-added to a new round of biological reduction of silica sand.

[0101] Circulation of organic acid wastewater: Similar to Example 11, the concentration of the obtained organic acid wastewater dropped to about half after 5 times of recycling. At this time, 1 / 2 of the previously added oxalic acid amount needed to be supplemented.

[0102] Recovery of organic acid: After the organic acid solution was recycled multiple times, when the concentration of free organic acid was lower than 40 mmol / L, Fe(III) coagulation recovery treatment was carried out.

[0103] Comparative Example 1: Use Shewanella sp.Bacterial reduction of Fe(OH)3

[0104] Take 0.216 g of FeCl3·6H2O and place it in a large beaker. Add 1 L of deionized water and stir magnetically until completely dissolved. Dropwise add saturated NaOH solution to adjust the pH to about 7.0 to obtain a yellowish-red-brown suspension. After standing for several hours with the pH unchanged, synthetic 0.8 mmol / L Fe(OH)3 is obtained. Add 120 mL of OD600 = 0.6 - 0.8 Shewanella sp. (after centrifugation) and 2.5 mL of 7 mol / L C3H5O3Na solution. Expose to high-purity nitrogen for more than 20 min and then seal and place in a 35 °C incubator for anaerobic reduction. Take 1 mL of water sample at 4 h and 7 d of reduction time to test its Fe(II) value.

[0105] Figure 18 The XRD pattern shows that Fe(OH)3 is amorphous. Without adding sulfur-containing compounds, reduction phenomenon starts to occur at 3 d of reduction; as Figure 14 shown, until the 7th d of reduction time, its Fe(III) reduction rate is 67.49%. However, after adding 2.5 mmol / L Na2S2O3 and reducing for 4 h, the suspension turns black and the Fe(III) reduction rate can reach 89.53%. Thus, it can be seen that adding sulfur-containing compounds can accelerate the reduction efficiency of Fe(III).

[0106] Comparative Example 2: Bacterial reduction of Fe2O3 without the participation of sulfides Shewanella sp. Bacterial reduction of Fe2O3

[0107] Take 100 mL of 0.8 mmol / L Fe2O3 suspension (Fe content is 89.6 mg / L), add OD600 = 0.6 - 0.8 Shewanella sp. bacteria (after centrifugation) and 2.5 mL of 7 mol / L C3H5O3Na solution. Adjust the pH value to 6.8 with 1 M dilute H2SO4 or saturated NaOH solution, seal and place in a 35 °C incubator for anaerobic reduction.

[0108] Figure 18 The XRD pattern shows that Fe2O3 is crystalline. As Figure 16 shown, without adding sulfur-containing compounds, for Fe2O3 with higher crystallinity after 10 days of reduction, the suspension still presents the reddish-brown color of the original Fe2O3, indicating that the reduction degree of Fe2O3 is very low.

[0109] Comparative Example 3: Bacterial reduction of Fe2O3 without the participation of sulfides Shewanella sp. Bacterial reduction of Fe2O3

[0110] Weigh 10 g of dried silica sand and add deionized water until the liquid level completely covers the silica sand. Add 120 mL of OD600 = 0.6 - 0.8 MR-1 (after centrifugation) and 2.5 mL of 7 mol / L C3H5O3Na solution. Do not add any sulfur-containing compounds. After purging with nitrogen to remove oxygen for more than 20 min, place it in an incubator at 35°C for anaerobic digestion, and observe the experimental phenomena every 12 h.

[0111] Most of the iron impurities in the silica sand adhere to its surface in the form of crystalline Fe2O3 films (as shown in the Raman diagram of iron-containing silica sand in Figure 18 ) or exist in the form of iron-containing minerals. As Figure 17 shown, in the case of not adding sulfide, the color of the iron-containing silica sand did not change after 15 days of reduction, indicating that Fe2O3 in the silica sand was not reduced.

[0112] As mentioned above, it is only the preferred embodiment of the present invention. The present invention is not limited to the above-mentioned implementation manners. As long as it achieves the technical effects of the present invention by the same or equivalent means, it should fall within the protection scope of the present invention. Within the protection scope of the present invention, various different modifications and changes can be made to its technical solutions and / or implementation manners.

Claims

1. A method for removing iron from silica sand by biological reduction, comprising the following steps: Iron-containing silica sand and Shewanella sp. The bacterial liquid is mixed, sodium lactate, a sulfur-containing compound and an electron mediator are added to obtain a mixed solution, the pH of the mixed solution is maintained at 6 to 7.5, and the mixed solution is placed in an anaerobic environment for 2 to 10 days; Separating solid matter from the mixed liquid to obtain reduced iron-containing silica sand; washing the reduced iron-containing silica sand with an organic acid solution at 20-100° C.; Wherein, the sulfur-containing compound is one or more of Na2S, Na2S2O3, elemental S, Na2SO3 and Na2SO4, and the concentration of the sulfur-containing compound in the mixed solution is 2.0~2.5 mmol / L; the electron mediator is humic acid or disodium anthraquinone-2,6-disulfonate.

2. The method according to claim 1, characterized in that Said Shewanella sp. The OD600 value of the bacterial solution was 0.6 ~ 0.

8.

3. The method according to claim 1, characterized in that The concentration of the sodium lactate in the mixed solution is 0.1-1 mol / L.

4. The method according to claim 1, characterized in that The organic acid solution is an oxalic acid aqueous solution.

5. The method according to claim 1, characterized in that: The biological reduction method for removing iron from silica sand also includes the step of recovering liquid substances in the mixed solution and repeatedly using the liquid substances for removing iron from silica sand.

6. The method according to claim 1, characterized in that The method for removing iron from silica sand by biological reduction also includes the step of recovering the organic acid solution and repeatedly using it for removing iron from silica sand.

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