Preparation method of calcium ion remover for drilling sewage and removal method

Abstract

The invention relates to a preparation method of a calcium ion remover for drilling sewage and a removal method, and the preparation method comprises the following steps: carrying out first reaction on a chitosan solution, an oxidizing agent and hydrophilic organic acid in a protective atmosphere, then adding an aldehyde cross-linking agent for second reaction, and then adjusting the pH value to obtain the calcium ion remover. The preparation method provided by the invention comprises the following steps: by taking chitosan as a parent and an oxidant as an initiator, reacting with hydrophilic organic acid for a certain time in a nitrogen atmosphere, then adding an aldehyde cross-linking agent, adjusting the pH after the reaction is finished, precipitating with an alcohol solution to obtain a reaction product, and drying the reaction product to obtain the calcium ion remover for drilling sewage. The preparation of the remover for selectively removing the calcium ions is realized; the drilling sewage treated by the agent meets the requirements of recycling and preparing fracturing fluid (Ca < 2 + > is less than or equal to 200mg / L, and TFe is less than or equal to 12.8 mg / L), and meets the fracturing fluid preparation standard.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and in particular to a preparation method and a removal method of a calcium ion remover for drilling sewage. Background Art

[0002] At present, with the continuous increase in the intensity of oil field development, a large amount of sewage will be continuously generated during the drilling operation. The presence and content of calcium ions in sewage directly affect the quality of recycled prepared water and the performance of prepared fracturing fluid. The hydroxyl groups on the guar gum molecular chain are easy to react with the calcium ions in the sewage to form precipitation, resulting in a significant decrease in the viscosity of the prepared guar gum base fluid. In addition, the preferential effect of calcium ions on the functional groups such as hydroxyl groups in the guar gum molecules leads to the need to replace calcium ions from the cross-linked calcium ion adducts when the organic boron cross-linking agent cross-links with the guar gum, resulting in a decrease in the cross-linking speed of the fracturing fluid, and even the viscosity of the fracturing fluid after cross-linking is also low; the increase in the calcium ion content in the sewage makes it easier for the gel-breaking fluid to form charged molecular clusters and attract each other, the resistance between the molecular movement in the gel-breaking fluid increases, and the viscosity of the gel-breaking fluid also increases accordingly. Guar gum cross-linked fracturing fluids are mostly weakly alkaline (pH 7.0-8.5). Calcium ions in weakly alkaline aqueous solutions easily absorb CO2 in the air to form carbonate precipitation, resulting in a significant increase in the amount of residue after gel-breaking. Therefore, how to effectively control or remove calcium ions in drilling wastewater has become an urgent problem that restricts the reuse of oilfield wastewater after treatment to prepare wellbore working fluid (such as fracturing fluid).

[0003] At present, the calcium ion treatment technologies in oilfield wastewater mainly include: chemical precipitation, coagulation / flocculation, chelation / complexation, shielding / masking, etc.

[0004] Chemical precipitation methods commonly use reagents such as lime, hydroxide, and sulfide. The principle is to add alkaline substances to sewage to adjust its pH value to make the solution alkaline. At this time, calcium and magnesium ions in the solution form hydroxides, which are then precipitated and separated. Dan Qiaoli et al. pumped the produced water from the tight oil layer into a flocculation sedimentation tank after being lifted by a peristaltic pump, and added chemical precipitants in turn for mixing, reaction, and precipitation. After adjusting the pH value to 7-7.5, it entered the intermediate water tank and was pumped for secondary filtration, so that calcium and magnesium ions were removed from the produced water of a tight oil layer in Changqing Oilfield. For example, CN110589991A provides a method for removing calcium ions from high-concentration organic wastewater, by introducing high-concentration organic wastewater containing calcium ions, an inorganic carbon source, and a seed crystal into a reactor, with a molar ratio of calcium ions to inorganic carbon of 1:(3.2-6.2), and adjusting the α(H + ) and ionic strength, stirring and precipitation are carried out in the reactor in sequence, and calcium ions in high-concentration organic wastewater are converted into calcium carbonate crystals, which are then precipitated and removed. Although the chemical precipitation method is simple to operate, a large amount of waste residue is generated during the process, causing secondary pollution.

[0005] The inorganic coagulants / flocculants (mainly aluminum salts and iron salts, etc.) used in the coagulation / flocculation method can destabilize impurities, colloids and fine suspended particles in sewage to form flocculent precipitation, thereby achieving impurity removal and water purification. Inorganic coagulants / flocculants have strong charge neutralization capabilities and low prices, and are widely used in the field of sewage treatment. However, the flocs produced are small and unstable, and the flocculation rate is slow, which easily causes metal ions (aluminum, iron, etc.) to remain in the water body; for example, CN112811613A discloses a water purification agent for efficiently removing calcium and magnesium ions in wastewater, the agent consists of a water purification agent and an auxiliary agent: the water purification agent consists of 50-70wt% sodium phosphate, 20-40wt% sodium carbonate and 5-10wt% polyaluminum chloride; the auxiliary agent is an anionic polyacrylamide aqueous solution, and the auxiliary agent is used in an amount of 0.1-0.5wt% of the water purification agent. The water purification agent effectively increases the precipitation rate and stability of calcium and magnesium ions in wastewater, reduces the volume of precipitates, and improves the use effect of the water purification agent. However, the use of sodium phosphate, polyaluminum chloride and polyacrylamide still has problems such as toxic monomers, residual aluminum ions, and difficulty in biodegradation.

[0006] The polymer chelating flocculants, chelating resins, chelating separation membranes, etc. used in the chelation / complexation method not only have strong adsorption capacity for heavy metal ions (copper, lead, chromium and nickel, etc.), but also have large chelation capacity. Gao Feng et al. developed the RXM-1 ion treatment agent suitable for the recovery and reuse of guar fracturing flowback fluid by compounding large-capacity chelating agents, high-efficiency bactericides, and temperature-resistant enhancers. This treatment agent can form water-soluble chelates with metal ions such as calcium and magnesium, but the operation and maintenance costs are relatively high. The complexing and solubilizing effect and the coagulation and dispersion effect of scale inhibitors (organic phosphonates, polycarboxylic acids, etc.) can capture calcium and magnesium ions in water to form stable complexes, which is equivalent to increasing the solubility of calcium and magnesium salts. However, due to its phosphorus-containing and non-degradable characteristics, its accumulation after large-scale use causes eutrophication of water bodies and harms the ecological environment.

[0007] Although masking agents (inorganic and organic masking agents) can effectively eliminate the influence of interfering ions such as calcium and magnesium, their pH usage conditions are strict, resulting in a limited scope of application and inability to be widely used.

[0008] In summary, the existing calcium ion treatment technology for drilling wastewater still has the problems of poor removal effect and low selectivity of calcium ions during the removal process. Summary of the invention

[0009] In view of the problems existing in the prior art, the purpose of the present invention is to provide a preparation method and removal method of a calcium ion remover for drilling wastewater, so as to solve the problems of poor removal effect and low selectivity of calcium ions during the removal process.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a method for preparing a calcium ion remover for drilling wastewater, the preparation method comprising:

[0012] The chitosan solution, the oxidant and the hydrophilic organic acid are subjected to a first reaction under a protective atmosphere, and then an aldehyde cross-linking agent is added to conduct a second reaction, and then the pH value is adjusted to obtain a calcium ion remover.

[0013] The preparation method provided by the present invention comprises the following steps: using chitosan as a matrix and an oxidant as an initiator, reacting with a hydrophilic organic acid for a certain period of time under a nitrogen atmosphere, then adding an aldehyde cross-linking agent, adjusting the pH after the reaction, precipitating the reaction product with an alcohol solution, drying and crushing the reaction product to obtain the drilling wastewater calcium ion remover of the present invention; during use, the calcium ion remover is dissolved in a liquid to be treated, and the chelation effect of the calcium ion remover can be used to achieve selective removal of calcium ions; the chelated calcium ions form stable chelates and still exist in the aqueous phase, thereby avoiding the influence of calcium ions on subsequent backwater utilization; at the same time, the obtained calcium ion remover can also chelate and remove a certain amount of iron ions in the liquid phase; the drilling wastewater treated with the agent meets the requirements for preparing fracturing fluid for reuse and meets the fracturing fluid preparation standards.

[0014] As a preferred technical solution of the present invention, the chitosan solution is obtained by mixing acetic acid solution and chitosan.

[0015] Preferably, the mass concentration of the acetic acid solution is 2-3%.

[0016] Preferably, the liquid-to-solid ratio of the acetic acid solution to chitosan is (40-60):1 in mL / g.

[0017] As a preferred technical solution of the present invention, the added amount of the oxidant is 0.5-0.7 times the mass of chitosan in the chitosan solution.

[0018] Preferably, the oxidizing agent comprises a persulfate.

[0019] As a preferred technical solution of the present invention, the liquid-to-solid ratio of the hydrophilic organic acid to chitosan in the chitosan solution is (12-13):1 in mL / g.

[0020] Preferably, the hydrophilic organic acid comprises acrylic acid and / or methacrylic acid.

[0021] As a preferred technical solution of the present invention, the temperature of the first reaction is 60-80°C.

[0022] Preferably, the first reaction time is 3-4 hours.

[0023] As a preferred technical solution of the present invention, the mass concentration of the aldehyde cross-linking agent is 20-30%.

[0024] Preferably, the aldehyde cross-linking agent includes one or a combination of at least two of succindialdehyde, glutaraldehyde or adipaldehyde.

[0025] Preferably, the liquid-to-solid ratio of the aldehyde cross-linking agent to chitosan in the chitosan solution is (5-6):1 mL / g.

[0026] As a preferred technical solution of the present invention, the temperature of the second reaction is 40-60°C.

[0027] Preferably, the second reaction time is 1-1.5 h.

[0028] As a preferred technical solution of the present invention, the pH value is adjusted to adjust the pH value of the material to 7-8.

[0029] In a second aspect, the present invention provides a method for removing calcium ions in drilling wastewater, the removal method comprising: removing calcium ions in drilling wastewater using the calcium ion remover obtained by the preparation method described in the first aspect.

[0030] The removal method comprises: adding the calcium ion remover into the drilling wastewater, stirring and dissolving the mixture, and then allowing the mixture to stand.

[0031] Preferably, the stirring speed during the stirring and dissolving is 50-100 r / min.

[0032] Preferably, the stirring and dissolving time is 15-30 min.

[0033] Preferably, the standing time is 20-40 min.

[0034] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0035] (1) The calcium ion remover of the present invention reduces the chelating effect of the remover on magnesium and iron ions in water by adding an aldehyde cross-linking agent to react with the amino group of chitosan, thereby improving its selective removal effect on calcium ions.

[0036] (2) The raw materials of the compound used in the present invention are easily available, the production process is simple, no toxic by-products are produced when the target calcium ions are removed, the impact on the environment is small, and it is safe and environmentally friendly.

[0037] (3) The calcium ion remover of the present invention is easy to use. Since a large number of hydrophilic groups are grafted onto chitosan, the calcium ion remover can be added to calcium-containing wastewater and stirred to dissolve, thereby effectively increasing the removal rate of free calcium ions in the wastewater, and has the advantage of simple operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1is an infrared spectrum of the calcium ion remover obtained in Example 1 of the present invention;

[0039] Figure 2 It is the infrared spectrum of the calcium ion remover obtained in Example 2 of the present invention.

[0040] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims. DETAILED DESCRIPTION

[0041] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0042] This embodiment provides a method for preparing a calcium ion remover for drilling wastewater, the preparation method comprising:

[0043] The chitosan solution, the oxidant and the hydrophilic organic acid are subjected to a first reaction under a protective atmosphere, and then an aldehyde cross-linking agent is added to conduct a second reaction, and then the pH value is adjusted to obtain a calcium ion remover.

[0044] In the present invention, the protective atmosphere is an atmosphere that does not participate in the reaction, such as nitrogen, helium, argon, neon and other protective gases that meet the requirements of the present invention.

[0045] In the present invention, the material after adjusting the pH value is precipitated with alcohol solution, and then dried and crushed to obtain a solid product of calcium ion remover. When used, the calcium ion remover is dissolved in the liquid to be treated to achieve chelation and shielding of calcium ions.

[0046] In the present invention, when the hydrophilic organic acid is added, the material temperature is raised to the first reaction temperature, and then the protective gas is replaced for 30-40 minutes before adding the hydrophilic organic acid.

[0047] In the present invention, the aldehyde cross-linking agent is added by dripping to ensure the cross-linking reaction effect.

[0048] Specifically, the chitosan solution is obtained by mixing acetic acid solution and chitosan.

[0049] Among them, the mass concentration of the acetic acid solution is 2-3%, for example, it can be 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9% or 3%, but is not limited to the listed values, and other unlisted values ​​within this range also meet the requirements.

[0050] Wherein, the liquid-to-solid ratio of the acetic acid solution and chitosan mL / g is (40-60):1, for example, it can be 40:1, 42:1, 44:1, 46:1, 48:1, 50:1, 52:1, 54:1, 56:1, 58:1 or 60:1, but is not limited to the listed values, and other values ​​not listed within the range also meet the requirements.

[0051] Specifically, the amount of the oxidant added is 0.5-0.7 times the mass of chitosan in the chitosan solution, for example, it can be 0.5 times, 0.52 times, 0.54 times, 0.56 times, 0.58 times, 0.6 times, 0.62 times, 0.64 times, 0.66 times, 0.68 times or 0.7 times, but is not limited to the listed values, and other unlisted values ​​within this range also meet the requirements.

[0052] Specifically, the oxidizing agent includes persulfate.

[0053] Wherein, the persulfate includes one or a combination of at least two of potassium persulfate, sodium persulfate or ammonium persulfate.

[0054] Specifically, the liquid-to-solid ratio of the hydrophilic organic acid to chitosan in the chitosan solution, mL / g, is (12-13):1, for example, it can be 12:1, 12.1:1, 12.2:1, 12.3:1, 12.4:1, 12.5:1, 12.6:1, 12.7:1, 12.8:1, 12.9:1 or 13:1, etc., but is not limited to the listed values, and other values ​​not listed within the range also meet the requirements.

[0055] Wherein, the hydrophilic organic acid includes acrylic acid and / or methacrylic acid.

[0056] Specifically, the temperature of the first reaction is 60-80°C, for example, it can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0057] Specifically, the time of the first reaction is 3-4 h, for example, 3 h, 3.2 h, 3.4 h, 3.6 h, 3.8 h or 4 h, etc., but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0058] Specifically, the aldehyde cross-linking agent includes one or a combination of at least two of succindialdehyde, glutaraldehyde or adipaldehyde.

[0059] In the present invention, the mass concentration of the aldehyde crosslinking agent is 20-30%, for example, it can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%, etc., but is not limited to the listed values, and other unlisted values ​​within this range also meet the requirements.

[0060] In the present invention, the aldehyde cross-linking agent is prepared using water or other commonly used solvents in the art.

[0061] In the present invention, the liquid-to-solid ratio of the aldehyde crosslinking agent to chitosan in the chitosan solution is (5-6):1, for example, it can be 5:1, 5.1:1, 5.2:1, 5.3:1, 5.4:1, 5.5:1, 5.6:1, 5.7:1, 5.8:1, 5.9:1 or 6:1, but is not limited to the listed values, and other values ​​not listed within the range also meet the requirements.

[0062] Specifically, the temperature of the second reaction is 40-60°C, for example, it can be 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0063] Specifically, the time of the second reaction is 1-1.5 h, for example, it can be 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h or 1.5 h, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0064] Specifically, the pH value is adjusted to adjust the pH value of the material to 7-8, for example, it can be 7, 7.2, 7.4, 7.6, 7.8 or 8, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0065] The selective remover obtained by the present invention can be used for the selective chelation of free calcium ions in aqueous solution, such as achieving hard water softening, or the chelation removal or shielding of free calcium ions in drilling wastewater, so that the recycled water has no effect on subsequent processes, thereby ensuring the stability of drilling operations or fracturing operations.

[0066] Furthermore, the present invention provides a method for removing free calcium ions in drilling wastewater, the removal method comprising: removing calcium ions in drilling wastewater using the calcium ion remover obtained by the preparation method as described above.

[0067] The calcium ion concentration in the drilling wastewater is >1000 mg / L, and the iron ion concentration (including Fe 3+ and Fe 2+ )>30mg / L.

[0068] Specifically, the removal method comprises: adding the calcium ion remover into the drilling wastewater, stirring and dissolving, and then allowing to stand;

[0069] The stirring speed in the stirring dissolution is 50-100 r / min, for example, it can be 50 r / min, 60 r / min, 70 r / min, 80 r / min, 90 r / min or 100 r / min, but is not limited to the listed values, and other values ​​not listed within the range also meet the requirements.

[0070] The stirring and dissolving time is 15-30 min, for example, 15 min, 20 min, 25 min or 30 min, but is not limited to the listed values, and other values ​​not listed within the range also meet the requirements.

[0071] The standing time is 20-40 min, for example, 20 min, 25 min, 30 min, 35 min or 40 min, but is not limited to the listed values, and other values ​​not listed within the range also meet the requirements.

[0072] In order to further illustrate the excellent performance of the calcium ion remover obtained by the preparation method of the calcium ion remover provided by the present invention, the following specific examples are provided, which are as follows:

[0073] Example 1

[0074] This embodiment provides a method for preparing a calcium ion remover for drilling wastewater, the preparation method comprising:

[0075] The chitosan solution, the oxidant and the hydrophilic organic acid are subjected to a first reaction under a protective atmosphere, and then an aldehyde cross-linking agent is added to conduct a second reaction, and then the pH value is adjusted to obtain a calcium ion remover;

[0076] The chitosan solution is obtained by mixing an acetic acid solution and chitosan; the mass concentration of the acetic acid solution is 2.5%; the liquid-to-solid ratio of the acetic acid solution to chitosan is 55:1 mL / g;

[0077] The amount of the oxidant added is 0.6 times the mass of chitosan in the chitosan solution; the oxidant is potassium persulfate;

[0078] The liquid-to-solid ratio of the hydrophilic organic acid to chitosan in the chitosan solution is 12.4:1 mL / g; the hydrophilic organic acid is methacrylic acid;

[0079] The temperature of the first reaction is 68° C.; the time of the first reaction is 4 hours;

[0080] The mass concentration of the aldehyde cross-linking agent is 24%; the aldehyde cross-linking agent is glutaraldehyde; the liquid-to-solid ratio of the aldehyde cross-linking agent to chitosan in the chitosan solution is 5.8:1 mL / g;

[0081] The temperature of the second reaction is 58°C; the time of the second reaction is 1.4h;

[0082] The pH value is adjusted to 7.

[0083] The infrared spectrum of the obtained calcium ion remover is as follows: Figure 1 As shown in the figure, after chitosan is grafted with acrylic acid, the characteristic stretching vibration peaks at 3417.38cm-1, 1260.85cm-1, and 1030.22cm-1 are attributed to the -OH group; the characteristic absorption peaks at 2963.92cm-1 and 1451.55cm-1 are attributed to the -CH3 and -CH2 groups, respectively; the characteristic stretching vibration peaks at 1721.18cm-1 and 1631.35cm-1 are attributed to the -COOH group, indicating the presence of polyacrylic acid in the synthetic product, which means that methacrylic acid is successfully grafted with chitosan; 1505.88cm-1 -1 and 1402.70cm -1 The characteristic absorption peak attributable to the C=NH group indicates that the grafted chitosan and aldehydes are successfully cross-linked and modified.

[0084] Example 2

[0085] This embodiment provides a method for preparing a calcium ion remover for drilling wastewater, the preparation method comprising:

[0086] The chitosan solution, the oxidant and the hydrophilic organic acid are subjected to a first reaction under a protective atmosphere, and then an aldehyde cross-linking agent is added to conduct a second reaction, and then the pH value is adjusted to obtain a calcium ion remover;

[0087] The chitosan solution is obtained by mixing an acetic acid solution and chitosan; the mass concentration of the acetic acid solution is 2.8%; the liquid-to-solid ratio of the acetic acid solution to chitosan is 50:1 mL / g;

[0088] The amount of the oxidant added is 0.54 times the mass of chitosan in the chitosan solution; the oxidant is sodium persulfate;

[0089] The liquid-to-solid ratio of the hydrophilic organic acid to chitosan in the chitosan solution is 12.8:1 mL / g; the hydrophilic organic acid is acrylic acid;

[0090] The temperature of the first reaction is 80° C.; the time of the first reaction is 3.5 h;

[0091] The mass concentration of the aldehyde cross-linking agent is 28%; the aldehyde cross-linking agent is glutaraldehyde; the liquid-to-solid ratio of the aldehyde cross-linking agent to chitosan in the chitosan solution is 5.5:1 mL / g;

[0092] The temperature of the second reaction is 45°C; the time of the second reaction is 1.2h;

[0093] The pH value is adjusted to 8.

[0094] The infrared spectrum of the obtained calcium ion remover is as follows: Figure 2 As shown, after chitosan was grafted with acrylic acid, 3434 cm -1 , 1430cm-1 and 1106cm-1 -1 The characteristic stretching vibration peak at 2947cm-1 is attributed to the -OH group; -1 and 1229cm -1 The characteristic absorption peaks at 1725cm-1 are respectively attributed to -CH3 and -CH2 groups; -1 、1570cm -1 and 1315cm -1 1157cm -1 and 1106cm -1 The characteristic absorption peak at 1530cm-1 belongs to the COC group, indicating that acrylic acid is successfully grafted onto chitosan. -1 and 1407cm -1 The characteristic absorption peak at 690 cm-1 is attributed to the C=NH group, indicating that the grafted chitosan and aldehydes are successfully cross-linked and modified. -1 If a weak peak appears at the position above, it indicates that the remover contains polyacrylate with multiple methylene chains.

[0095] Example 3

[0096] This embodiment provides a method for preparing a calcium ion remover for drilling wastewater, the preparation method comprising:

[0097] The chitosan solution, the oxidant and the hydrophilic organic acid are subjected to a first reaction under a protective atmosphere, and then an aldehyde cross-linking agent is added to conduct a second reaction, and then the pH value is adjusted to obtain a calcium ion remover;

[0098] The chitosan solution is obtained by mixing an acetic acid solution and chitosan; the mass concentration of the acetic acid solution is 2%; the liquid-to-solid ratio of the acetic acid solution to chitosan is 60:1 mL / g;

[0099] The amount of the oxidant added is 0.7 times the mass of chitosan in the chitosan solution; the oxidant is ammonium persulfate;

[0100] The liquid-to-solid ratio of the hydrophilic organic acid to chitosan in the chitosan solution is 13:1 mL / g; the hydrophilic organic acid is acrylic acid;

[0101] The temperature of the first reaction is 80° C.; the time of the first reaction is 3 h;

[0102] The mass concentration of the aldehyde cross-linking agent is 30%; the aldehyde cross-linking agent is glutaraldehyde; the liquid-to-solid ratio of the aldehyde cross-linking agent to chitosan in the chitosan solution is 5:1 mL / g;

[0103] The temperature of the second reaction is 40° C.; the time of the second reaction is 1.5 h;

[0104] The pH value is adjusted to 7.5.

[0105] Example 4

[0106] This embodiment provides a method for preparing a calcium ion remover for drilling wastewater, the preparation method comprising:

[0107] The chitosan solution, the oxidant and the hydrophilic organic acid are subjected to a first reaction under a protective atmosphere, and then an aldehyde cross-linking agent is added to conduct a second reaction, and then the pH value is adjusted to obtain a calcium ion remover;

[0108] The chitosan solution is obtained by mixing an acetic acid solution and chitosan; the mass concentration of the acetic acid solution is 3%; the liquid-to-solid ratio of the acetic acid solution to chitosan is 40:1 mL / g;

[0109] The amount of the oxidant added is 0.5 times the mass of chitosan in the chitosan solution; the oxidant is potassium persulfate;

[0110] The liquid-to-solid ratio of the hydrophilic organic acid to chitosan in the chitosan solution is 12:1 mL / g; the hydrophilic organic acid is acrylic acid and methacrylic acid in a mass ratio of 1:1;

[0111] The temperature of the first reaction is 60° C.; the time of the first reaction is 4 hours;

[0112] The mass concentration of the aldehyde cross-linking agent is 20%; the aldehyde cross-linking agent is glutaraldehyde; the liquid-to-solid ratio of the aldehyde cross-linking agent to chitosan in the chitosan solution is 6:1 mL / g;

[0113] The temperature of the second reaction is 50°C; the time of the second reaction is 1 hour;

[0114] The pH value is adjusted to 7.

[0115] In order to illustrate the calcium ion removal performance of the calcium ion remover obtained in Examples 1-4, the calcium ion remover was used to remove the drilling wastewater, as follows:

[0116] The calcium ion remover was added to the drilling wastewater and stirred and dissolved for 20 minutes, and then allowed to stand for 20 minutes; the stirring speed during the stirring and dissolving was 50 r / min; the concentrations of calcium ions and iron ions in the supernatant were detected to evaluate the removal effect of the calcium ion remover, and the results are shown in Table 1.

[0117] Among them, the concentrations of calcium ions and iron ions in the raw drilling wastewater are 1000 mg / L and 28 mg / L respectively.

[0118] Table 1

[0119]

[0120]

[0121] The results of the above examples show that the preparation method provided by the present invention uses chitosan as a matrix and an oxidant as an initiator, reacts with a hydrophilic organic acid under a nitrogen atmosphere for a certain period of time, then adds an aldehyde cross-linking agent, adjusts the pH after the reaction, and precipitates the reaction product with an alcohol solution, and then dries and crushes it to obtain the drilling wastewater calcium ion remover of the present invention, which realizes the selective removal of calcium ions; the drilling wastewater treated with this agent meets the requirements of reuse for preparing fracturing fluid (Ca 2+ ≤200mg / L, TFe≤12.8mg / L), which meets the preparation standards of fracturing fluid.

[0122] It is stated that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0123] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0124] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0125] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing a calcium ion remover for drilling wastewater, characterized in that: The preparation method comprises: The chitosan solution, the oxidant and the hydrophilic organic acid are subjected to a first reaction under a protective atmosphere, and then an aldehyde cross-linking agent is added to conduct a second reaction, and then the pH value is adjusted to obtain a calcium ion remover.

2. The preparation method according to claim 1, characterized in that: The chitosan solution is obtained by mixing acetic acid solution and chitosan; Preferably, the mass concentration of the acetic acid solution is 2-3%; Preferably, the liquid-to-solid ratio of the acetic acid solution to chitosan is (40-60) mL / g:

1.

3. The preparation method according to claim 1 or 2, characterized in that: The amount of the oxidant added is 0.5-0.7 times the mass of chitosan in the chitosan solution; Preferably, the oxidizing agent comprises a persulfate.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The liquid-to-solid ratio of the hydrophilic organic acid to chitosan in the chitosan solution is (12-13) mL / g:1; Preferably, the hydrophilic organic acid comprises acrylic acid and / or methacrylic acid.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The temperature of the first reaction is 60-80°C; Preferably, the first reaction time is 3-4 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The mass concentration of the aldehyde cross-linking agent is 20-30%; Preferably, the aldehyde cross-linking agent comprises one or a combination of at least two of succindialdehyde, glutaraldehyde or adipaldehyde; Preferably, the liquid-to-solid ratio of the aldehyde cross-linking agent to chitosan in the chitosan solution is (5-6):1 mL / g.

7. The preparation method according to any one of claims 1 to 7, characterized in that: The temperature of the second reaction is 40-60°C; Preferably, the second reaction time is 1-1.5 h.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The pH value is adjusted to 7-8.

9. A method for removing calcium ions from drilling wastewater, characterized in that: The removal method comprises: removing calcium ions in drilling wastewater using a calcium ion remover obtained by the preparation method according to any one of claims 1 to 8.

10. The removal method according to claim 9, characterized in that: The removal method comprises: adding the calcium ion remover into drilling wastewater, stirring and dissolving the mixture, and then allowing the mixture to stand; Preferably, the stirring speed in the stirring and dissolving is 50-100 r / min; Preferably, the stirring and dissolving time is 15-30 min; Preferably, the standing time is 20-40 min.

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