A composite flocculant for treating wastewater coexisting with multiple heavy metals and a preparation method thereof

Abstract

This invention discloses a composite flocculant for treating wastewater containing multiple heavy metals and its preparation method, belonging to the field of wastewater treatment technology. The composite flocculant comprises modified pectin, modified shellac, tartaric acid-bentonite complex, cinnamic acid-oxygenated xylan, galacturonic acid, trehalose-pectinase complex, and activated zeolite powder. The modified pectin is obtained by modifying pectin with oxalic acid; the modified shellac is obtained by modifying shellac with lactic acid; the cinnamic acid-oxygenated xylan is prepared by acylation of xylan with cinnamic anhydride; and the activated zeolite powder is prepared by activating natural zeolite with sodium bicarbonate solution. Through the synergistic effect of its components, this invention can effectively remove key pollutants such as heavy metals, ammonia nitrogen, cyanide, sulfides, and tannins from wastewater, improve floc settling performance, reduce scum formation, and ensure that the pollutant levels in the treated water meet the requirements for agricultural irrigation and temporary miscellaneous water use.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically a composite flocculant for treating wastewater containing multiple heavy metals and its preparation method. Background Technology

[0002] The Qinling-Bashan Mountains in northern Sichuan and the mountainous valleys bordering Sichuan and Gansu are characterized by high mountains, deep valleys, and fragmented terrain. Small ecological resettlement sites, remote forest rangers, and scattered farmers rely primarily on a mixture of mountain streams and shallow groundwater for their temporary domestic water needs (such as toilet flushing, farm tool washing, and yard cleaning), as well as for irrigation of surrounding farmland. Two typical types of pollution exist in this area: first, scattered livestock and poultry farming activities along the river, mainly free-range cattle, sheep, and poultry, with wastewater flowing into streams via surface runoff; second, scattered abandoned mining sites and smelting remnants from the past, including tailings piles and mined-out areas from lead-zinc mines, small coal mines, and mercury mines, as well as simple smelting slag heaps and abandoned furnaces. Due to their age, these sites lack effective seepage prevention measures. During the rainy season, rainwater leaches mineral slag and rock strata, forming leachate containing low concentrations of heavy metals, which then flows into streams, creating a complex pollution system. Due to the complex composition of this water body, simple treatment methods such as sedimentation and simple filtration, as well as inorganic flocculant treatment technologies such as polyaluminum chloride, are poorly adapted and cannot be treated to meet the basic water quality requirements for farmland irrigation and temporary miscellaneous water use. This poses a potential impact on the safety of farmland irrigation and temporary domestic miscellaneous water use in the region. It will not only exacerbate soil heavy metal pollution and affect crop growth, but may also seep into the human body through skin contact, causing adverse effects on human health.

[0003] The primary challenge in treating such complexly polluted water bodies is the stable complexes formed by heavy metals and humic acid. Historical mining and smelting remains in the area release low concentrations of heavy metal ions, such as lead (0.05-0.2 mg / L), zinc (0.1-0.5 mg / L), cadmium (0.005-0.02 mg / L), and mercury (0.001-0.003 mg / L), into the water bodies through rainwater leaching. Meanwhile, the decomposition of fallen leaves from the mountain broadleaf forests produces humic acid. These two substances combine in the water through coordination bonds to form stable organic-heavy metal complexes. These complexed heavy metals are difficult to capture with conventional flocculants and cannot be removed by natural sedimentation, thus failing to effectively remove heavy metals from the water and threatening the safety of agricultural irrigation and temporary miscellaneous water use in the region.

[0004] The second challenge is the interference of ammonia nitrogen carried by livestock wastewater on the heavy metal complexation system. Wastewater from scattered livestock farming in the area flows into streams and ditches, carrying ammonia nitrogen. During the dry season, the concentration remains at 0.8-2.5 mg / L, while during the rainy season, due to the cumulative effect of surface runoff, the concentration can rise to 3.0-5.2 mg / L. Due to leaching from rock strata, the water body is weakly acidic, and ammonia nitrogen exists mainly in the form of ammonium ions under this environment. The coordination ability of ammonium ions and heavy metal ions differs significantly. Low concentrations of ammonium ions do not significantly compete with heavy metal-humic acid complexes, making it difficult to destroy the complex structure or promote the dissociation of heavy metals. However, it indirectly alters the ionic strength of the water body, resulting in loose flocs formed by conventional flocculants with poor settling performance. Furthermore, the synergistic pollution of ammonia nitrogen and heavy metals further exacerbates water quality deterioration. Conventional treatment methods cannot simultaneously remove both types of pollutants, ultimately leading to a decline in treatment efficiency and failing to meet the basic water quality requirements for farmland irrigation and temporary miscellaneous water use.

[0005] The third challenge is the persistent degradation of cyanide complexes. Some historical small-scale gold mines in the region used cyanide extraction. After the mines closed, residual reagents slowly release trace amounts of cyanide into the water, typically at concentrations of 0.02-0.05 mg / L, with peak leaching levels reaching 0.06-0.08 mg / L during the rainy season. These cyanides combine with heavy metal ions in the water to form [Zn(CN)4]. 2- [Cd(CN)4] 2- These are metal cyanide complexes. These complexes are chemically stable and resistant to conventional degradation processes such as sodium hypochlorite oxidation. They are also difficult to retain by conventional inorganic and organic flocculants, and simple treatment methods commonly used by residents, such as sedimentation and filtration, have little effect on them.

[0006] The fourth challenge is the difficulty in removing the complex system formed by tannins combined with heavy metals and sulfides. Along the river valleys of the Qinling-Bashan Mountains in northern Sichuan, broad-leaved trees such as oak and birch are widely grown. In autumn and winter, large amounts of fallen leaves enter the water and decompose, producing tannins. Simultaneously, leachate from abandoned small coal mines introduces trace amounts of sulfides (S²⁻ concentration 0.01-0.05 mg / L). These sulfides, along with lead and zinc ions, readily form trace sulfide precipitates in weakly acidic natural water due to their extremely low solubility. Some of these precipitates remain suspended as fine particles due to water disturbance and tannin adsorption. Tannins form coordination bonds with heavy metal ions through their phenolic hydroxyl groups, and simultaneously bind to fine sulfide particles through hydrogen bonds and hydrophobic interactions, ultimately forming a colloidal complex particle system. This system not only resists the complex-breaking and adsorption effects of conventional flocculants, but also encapsulates the flocs formed by the flocculants, hindering the growth and sedimentation of the flocs. This makes it difficult for conventional flocculation processes to effectively remove such complex pollutants, and thus cannot guarantee the water quality safety of farmland irrigation and temporary miscellaneous water use.

[0007] Therefore, developing a composite flocculant that can alleviate the above-mentioned technical difficulties is of great practical significance for improving the water quality safety of local farmland irrigation and temporary domestic miscellaneous water use. Summary of the Invention

[0008] The purpose of this invention is to provide a composite flocculant for treating wastewater containing multiple heavy metals and its preparation method, specifically addressing the problem of treating composite heavy metal wastewater in remote areas such as the Qinba Mountains in northern Sichuan. It effectively removes multiple pollutants such as heavy metals, ammonia nitrogen, cyanide, sulfide, and tannins from water bodies, providing a reliable guarantee for the safety of local farmland irrigation and temporary miscellaneous water use.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A composite flocculant for treating wastewater containing multiple heavy metals comprises the following components by weight: 25-30 parts modified pectin, 18-22 parts modified shellac, 20-25 parts tartaric acid-bentonite complex, 10-15 parts cinnamicylated xylan, 5-10 parts galacturonic acid, 0.5-1 part trehalose-pectinase complex, and 2-3 parts activated zeolite powder;

[0011] The modified pectin is obtained by modifying pectin with oxalic acid, and the carboxyl content of the modified pectin is 12%-15%.

[0012] The modified shellac is obtained by modifying shellac with lactic acid;

[0013] The cinnamic-acylated xylan is prepared by acylation of xylan with cinnamic anhydride, and the degree of substitution of the cinnamic-acylated xylan is 0.15-0.20.

[0014] The carboxyl content of the modified pectin was determined by acid-base potentiometric titration; the degree of substitution of cinnamic acylated xylan was determined by ¹H-NMR.

[0015] The activated zeolite powder is made from natural zeolite activated with sodium bicarbonate solution;

[0016] The pollutants in the wastewater include heavy metals, ammonia nitrogen, cyanide, sulfides, and tannins.

[0017] In the above scheme, the functions of each component are as follows:

[0018] Pectin possesses a large molecular skeleton structure and contains natural carboxyl groups, which can form coordination bonds with some free heavy metal ions in water. It can also adsorb suspended fine particles in water, exhibiting basic flocculation and heavy metal adsorption capabilities. After modification with oxalic acid, the pectin molecular chain can be degraded to a certain extent, improving its water solubility. This exposes its inherent carboxyl groups, enhancing its coordination and binding capacity with heavy metal ions. By preferentially coordinating with complexed heavy metal ions, it can compete for the binding sites of humic acid on heavy metal ions, indirectly promoting the dissociation of heavy metal-humic acid complexes and thus capturing the dissociated heavy metal ions.

[0019] Shellac itself contains active groups such as ester and hydroxyl groups, possessing a certain adsorption and encapsulation capacity, and can adsorb small amounts of free heavy metal ions. Specifically, the carboxyl groups introduced after lactic acid modification of shellac can coordinate and bind with heavy metal ions in cyanide complexes in water. The shellac macromolecular framework simultaneously encapsulates these complexes, forming relatively stable primary particles that facilitate subsequent adsorption and sedimentation. This also enhances the hydrophobicity of the entire flocculation system, aiding in improved floc aggregation and reducing floc loosening. Lactic acid modification slightly improves the swelling properties of shellac in weakly acidic wastewater environments. The carboxyl groups of lactic acid adsorbed on the shellac surface impart a weak negative charge, aiding in uniform dispersion. Furthermore, the natural tannins present in the wastewater can form hydrogen bonds with the hydroxyl groups of shellac, further improving its dispersion.

[0020] Bentonite exhibits excellent adsorption properties and a nucleation effect, enabling it to adsorb small amounts of heavy metal ions in water and support floc formation. After modification with tartaric acid, its synergistic compatibility with bio-based components (modified pectin, modified shellac, etc.) is enhanced, and its adsorption selectivity is also improved. It can adsorb dissociated heavy metal ions and primary particles encapsulated in shellac, while also adsorbing some fine sulfide particles captured by cinnamyl xylan. Simultaneously, it provides stable nucleation anchoring points for floc formation, facilitating rapid floc formation and aggregation, improving sedimentation efficiency, and achieving simultaneous removal of fine sulfide particles.

[0021] Xylan contains a large number of polyhydroxyl groups, which can adsorb small amounts of polar pollutants in water. After cinnamic anhydride acylation modification, a hydrophobic benzene ring and active double bonds are introduced into its molecule. The polyhydroxyl groups can form a hydrogen bond network with partially dissociated humic acid in the water, while the hydrophobic benzene ring can bind some humic acid through hydrophobic interactions. The two work synergistically to fix some free humic acid, reducing the probability of it re-binding with heavy metal ions to form complexes. At the same time, the hydrophobic benzene ring can adsorb some of the natural tannins contained in the wastewater, as well as some temporary coordination complexes formed by tannins and heavy metal ions, reducing the possibility of it forming secondary complex colloids with heavy metals and sulfides.

[0022] The carboxyl groups in galacturonic acid can neutralize the charge of ammonium ions in wastewater, stabilize the ionic strength of the water, and reduce the interference of ammonium ions on the settling performance of flocs. Galacturonic acid is highly water-soluble; if not fully fixed, a small amount of free residue may remain. The layered porous structure of the tartaric acid-bentonite complex can physically adsorb free galacturonic acid, and the macromolecular chains of modified pectin can bind to galacturonic acid through hydrogen bonds, resulting in dual fixation and reduced residue.

[0023] The trehalose-pectinase complex is composed of pectinase and trehalose through hydrogen bonding. Pectinase can regulate the moderate degradation of modified pectin in water, avoiding floc aggregation caused by excessively long modified pectin molecular chains, and helping to form uniform flocs. Trehalose forms a stable hydrogen bond network with enzyme molecules, effectively inhibiting enzyme aggregation and inactivation. At the same time, it can synergistically work with the polar groups of galacturonic acid to indirectly alleviate the local hydrophobicity of cinnamicyl xylan, optimize the hydrophilic-hydrophobic balance of the system, and reduce the generation of floc scum.

[0024] Zeolite can adsorb small amounts of small-molecule pollutants and suspended particles in water. After activation with sodium bicarbonate solution, surface impurities are removed, pore size is expanded, and physical adsorption performance is further optimized, enabling it to adsorb some residual trace heavy metal ions and other small-molecule pollutants in the water. Simultaneously, sodium bicarbonate can buffer the pH of wastewater, reducing the impact of abnormal water acidity on flocculation.

[0025] In summary, this application, through the synergistic effect of its components, can improve the problems existing in conventional flocculants when treating wastewater containing multiple heavy metals, such as poor removal of complexed heavy metals, poor floc settling performance, and difficulty in adapting to complex water quality environments. It is suitable for complex wastewater treatment scenarios where multiple heavy metals coexist, and the core indicators such as heavy metals, ammonia nitrogen, and cyanide in the treated water can meet the basic requirements for farmland irrigation and temporary miscellaneous water use.

[0026] As some possible embodiments of this application, the tartaric acid-bentonite composite has a particle size of 150-200 mesh, and the mass ratio of tartaric acid to bentonite is 1:(8-10).

[0027] As some possible implementations of this application, in the trehalose-pectinase complex, the mass ratio of trehalose to pectinase is (15-20):(80-85).

[0028] As some possible embodiments of this application, the particle size of the activated zeolite powder is 200-300 mesh; the mass fraction of the sodium bicarbonate solution is 4-8%; and the solid-liquid ratio of zeolite to sodium bicarbonate solution is 1:(5-10), g:ml.

[0029] As one possible implementation of this application, in the cinnamicylated xylan, the mass ratio of xylan to cinnamic anhydride is 1:(0.3-0.5).

[0030] As one possible implementation of this application, in the modified pectin, the mass ratio of oxalic acid to pectin is 1:(12-15).

[0031] As one possible implementation of this application, in the modified shellac, the mass ratio of lactic acid to shellac is 1:(10-15).

[0032] As some possible embodiments of this application, the flocculant further includes 1.5-2.5 parts of potassium dihydrogen phosphate modified diatomaceous earth; the particle size of the potassium dihydrogen phosphate modified diatomaceous earth is 200-300 mesh. In actual flocculation, colloidal particles formed by the tannin-heavy metal-sulfide complex system in water are prone to entanglement and aggregation during floc formation, resulting in excessively high floc density and caking. Caking flocs are difficult to settle quickly and may also encapsulate some residual fine sulfide particles that have not been removed, affecting the water purification effect. At the same time, the trace amounts of fine sulfide particles remaining in the wastewater in the background technology cannot be fully removed by adsorption alone using tartaric acid-bentonite complex, which can easily cause pollutant residues and fail to better meet the water quality requirements for farmland irrigation and temporary miscellaneous water use. Based on this, this application adds potassium dihydrogen phosphate modified diatomaceous earth, which has a porous structure and active phosphate groups. It can interweave and build a loose skeleton during floc formation, reduce floc density to avoid caking, and help flocs settle quickly. At the same time, the phosphate groups on its surface can adsorb residual fine sulfide particles in the water, reduce pollutant residues, and further improve the water purification effect.

[0033] In addition, to achieve the above objectives, this application also provides a method for preparing a composite flocculant, comprising the following steps:

[0034] S1. Take the tartaric acid-bentonite complex, add deionized water and stir to make a suspension;

[0035] S2. Mix the modified pectin and modified shellac, add them to the suspension, heat to 40-45℃ and stir at a constant temperature. After stirring, cool to room temperature, add cinnamicyl xylan, galacturonic acid, trehalose-pectinase complex, and activated zeolite powder in sequence, stir thoroughly, and then dry and pulverize under vacuum at low temperature to obtain the flocculant.

[0036] As one possible implementation of this application, in step S2, the vacuum low-temperature drying temperature is <40°C.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] The composite flocculant provided by this invention can effectively treat complex wastewater containing heavy metals, ammonia nitrogen, cyanide, sulfide, and tannins. After treatment, the pollutant levels in the water meet the basic water quality requirements for farmland irrigation and temporary miscellaneous water use. Specifically, after treatment, the lead content in the water is ≤0.015 mg / L, zinc content ≤0.042 mg / L, cadmium content ≤0.0010 mg / L, and mercury content ≤0.0004 mg / L. This significantly reduces the content of various heavy metal ions in the water, lowering the risk of heavy metals seeping into the soil with irrigation water and affecting crop growth, as well as the risk of harming human health through skin contact. The cyanide content is ≤0.0032 mg / L, showing good retention of difficult-to-treat metal cyanide complexes, improving the problem of difficult removal of such pollutants. Ammonia nitrogen content is also reduced. With a content ≤0.48mg / L, ammonium ions help reduce interference with floc settling, making the ionic strength of the water more stable and creating favorable conditions for floc aggregation and settling. Sulfide content ≤0.0015mg / L reduces the residue of fine sulfide particles in the water, lowering the probability of them combining with heavy metals and tannins to form complex colloids. Humic acid content ≤1.12mg / L and tannin content ≤0.92mg / L help dismantle stable complexes formed by heavy metals and humic acid, while reducing excessive tannin residue and the possibility of secondary colloid formation. The water pH is stable between 6.3 and 6.7, meeting the pH requirements for crop growth and temporary miscellaneous water use. The floc settling speed is ≥1.6mm / min, the volume compression ratio is ≥62%, and no scum is generated, which can achieve rapid floc settling and facilitate subsequent cleaning, making it suitable for simple treatment scenarios in remote areas.

[0039] Overall, this composite flocculant effectively improves many problems existing in conventional flocculants in the treatment of complex wastewater through the synergistic effect of its components. Moreover, the preparation process is simple and easy to operate, and it has practical value in improving the water quality safety of local farmland irrigation and temporary domestic miscellaneous water use. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. Components for which preparation methods are not mentioned in the embodiments and comparative examples are all commercially available conventional products (such as galacturonic acid, bentonite, etc.). All "parts" refer to parts by mass. In industrial production, "kg" or "g" can be used as the unit of mass.

[0041] Example 1

[0042] 1. Preparation of non-commercially available components:

[0043] (1) Preparation of modified pectin: Pectin (esterification degree 65-70%, weight average molecular weight 100-150kDa) was mixed with deionized water at a mass ratio of 1:6 and ultrasonically dispersed for 20 min (power 300W, frequency 40kHz); then oxalic acid (mass ratio of oxalic acid to pectin is 1:13) was added, the pH was adjusted to 3.5, the temperature was raised to 50℃, and the mixture was stirred at a constant temperature of 180r / min for 1.5 h; then it was vacuum dried at low temperature (55℃) to constant weight and pulverized to 80 mesh to obtain modified pectin (carboxyl content 13.5%).

[0044] (2) Preparation of modified shellac: Shellac (acid value 60-70 mg KOH / g) and 70% ethanol aqueous solution were mixed at a mass ratio of 1:6, heated to 70℃, and stirred at 150 r / min for 30 min; then cooled to 30℃, lactic acid (mass ratio of lactic acid to shellac 1:12) was added, and the mixture was stirred at 160 r / min for 1 h of constant temperature modification; after modification, the mixture was dried under vacuum at low temperature (58℃) to constant weight, and pulverized to 80 mesh to obtain modified shellac (acid value 85-95 mg KOH / g, infrared spectrum at 1720 cm⁻¹). -1 (A characteristic absorption peak for carboxyl groups appears at this location).

[0045] (3) Preparation of tartaric acid-bentonite complex:

[0046] Natural bentonite (montmorillonite content ≥85%) and deionized water were mixed at a mass ratio of 1:5 and ultrasonically dispersed for 15 min (power 250W). Then, tartaric acid (tartaric acid to bentonite mass ratio of 1:9) was added, the pH was adjusted to 4.0, and the mixture was stirred at a constant temperature of 180 r / min at room temperature for 30 min. After that, it was dried under vacuum at low temperature (55℃) to constant weight and pulverized to 180 mesh to obtain tartaric acid-bentonite composite.

[0047] (4) Preparation of cinnamicylated xylan: Take 100 parts of xylan, add 500 parts of dimethyl sulfoxide (DMSO), and ultrasonically disperse for 20 min (power 300W); then add 40 parts of cinnamic anhydride and 0.5 parts of pyridine, heat to 65℃, stir at 180 r / min, and react at a constant temperature for 2 h; after the reaction is completed, cool to room temperature, filter and collect the solid, wash twice with anhydrous ethanol, dry under vacuum at low temperature (55℃) to constant weight, and pulverize to 80 mesh to obtain cinnamicylated xylan (degree of substitution 0.18).

[0048] (5) Preparation of trehalose-pectinase complex:

[0049] Take 82.5 parts of low molecular weight pectinase (endogalacturonase, enzyme activity 5000 U / g), add 400 parts of deionized water, and dissolve for 20 min at a low temperature (28℃) and a stirring speed of 150 r / min. Then add 17.5 parts of trehalose, maintain the temperature at 28℃, and stir at a speed of 120 r / min for 30 min. Then freeze-dry under vacuum (-40℃, vacuum degree ≤30 torr), and pulverize to 100 mesh to obtain trehalose-pectinase complex (enzyme activity ≥4500 U / g).

[0050] (6) Preparation of activated zeolite powder:

[0051] Natural zeolite and 5wt% sodium bicarbonate solution were mixed at a mass ratio of 1:7 and stirred at 160 r / min at room temperature for 2 h. After activation, the solid was collected by filtration, washed three times with deionized water, dried under vacuum at low temperature (55℃) to constant weight, and pulverized to 250 mesh to obtain activated zeolite powder.

[0052] 2. Preparation of composite flocculants:

[0053] S1. Take 22 parts of tartaric acid-bentonite complex, add 6 times its mass of deionized water, stir at room temperature (25℃) for 40 minutes at a stirring speed of 180 r / min to prepare a uniform suspension;

[0054] S2. Mix 28 parts of modified pectin and 20 parts of modified shellac evenly, add to the above suspension, heat to 42℃, stir at 200 r / min, and maintain the temperature for 50 min; then cool to 25℃, add 14 parts of cinnamylated xylan, stir at 180 r / min for 30 min; then add 6.5 parts of galacturonic acid, and continue stirring for 15 min; then add 0.7 parts of trehalose-pectinase complex, stir at 150 r / min for 25 min (low temperature slow stirring to protect enzyme activity); then add 2.5 parts of activated zeolite powder, stir at 180 r / min for 10 min to form a homogeneous colloidal flocculant, then dry at 30-35℃ and vacuum degree ≤30 torr until the moisture content is below 20%, then cool to 25℃ and continue vacuum drying to constant weight, then pulverize at low speed (300 r / min) using a universal pulverizer to 80 mesh powder, thus obtaining the composite flocculant.

[0055] Example 2

[0056] This embodiment differs from Example 1 in that the following parameters are adjusted during flocculant preparation (unless otherwise mentioned, in which case they are considered consistent with Example 1):

[0057] 25 parts modified pectin, 22 parts modified shellac, 20 parts tartaric acid-bentonite complex, 12 parts cinnamicylated xylan, 5 parts galacturonic acid, 0.5 parts trehalose-pectinase complex, and 3 parts activated zeolite powder.

[0058] Example 3

[0059] Compared to Example 1, in step S2 of the flocculant preparation, after adding activated zeolite powder and stirring, an additional 2 parts of potassium dihydrogen phosphate modified diatomaceous earth were added, the stirring speed was 160 r / min, and the stirring time was 8 min. The preparation process of the remaining non-commercial components, the flocculant preparation steps and parameters were the same as in Example 1.

[0060] The preparation process of the potassium dihydrogen phosphate modified diatomite is as follows:

[0061] Take 100 parts of natural diatomaceous earth, add 600 parts of 1wt% potassium dihydrogen phosphate solution, stir at 150 r / min at room temperature and activate for 1 h; after activation, filter to collect the solid, wash twice with deionized water, dry under vacuum at low temperature (55℃) to constant weight, and pulverize to 280 mesh to obtain potassium dihydrogen phosphate modified diatomaceous earth.

[0062] Comparative Example 1

[0063] Compared to Example 1, the modified pectin was replaced with an equal mass of unmodified pectin, and the modified shellac was replaced with an equal mass of unmodified shellac. The preparation processes of the other non-commercial components, the preparation steps of the flocculant, and the parameters were all the same as in Example 1.

[0064] Comparative Example 2

[0065] Compared to Example 1, the tartaric acid-bentonite complex was replaced with an equal mass of unmodified bentonite, while the preparation processes of the remaining non-commercial components, the flocculant preparation steps, and the parameters were the same as in Example 1.

[0066] Comparative Example 3

[0067] Compared to Example 1, the cinnamicylated xylan component was removed, while the preparation processes, flocculant preparation steps, and parameters of the remaining non-commercially available components were the same as in Example 1.

[0068] Comparative Example 4

[0069] Compared to Example 1, the trehalose-pectinase complex was replaced with an equal mass of unmodified pectinase, while the preparation processes of the remaining non-commercially available components, the flocculant preparation steps, and the parameters were the same as in Example 1.

[0070] Comparative Example 5

[0071] Compared to Example 1, the activated zeolite powder component was removed, while the preparation processes, flocculant preparation steps, and parameters of the remaining non-commercially available components were the same as in Example 1.

[0072] Comparative Example 6

[0073] Compared to Example 1, the modified shellac component was removed, while the preparation processes, flocculant preparation steps, and parameters of the remaining non-commercially available components were the same as in Example 1.

[0074] Comparative Example 7

[0075] The flocculant in Example 1 was replaced with a conventional inorganic flocculant composition (30 parts polyaluminum chloride, 20 parts ferrous sulfate, and 0.5 parts polyacrylamide, mixed evenly). The remaining flocculant preparation steps, wastewater treatment processes, and parameters were the same as in Example 1.

[0076] Experimental Example

[0077] The flocculants prepared in Examples 1-3 and Comparative Examples 1-7 were used to conduct experiments on the treatment of complex heavy metal wastewater. The water used in all experimental groups was the same batch of simulated complex heavy metal wastewater from the Qinba Mountains in northern Sichuan (specific indicators are shown in Table 1). The flocculant dosage was 0.3% of the wastewater mass. The treatment effect was detected after stirring at room temperature for 10 min and allowing the water to settle for 30 min. The floc settling speed, scum formation, and pH changes of the water were recorded. Each experiment was repeated 3 times, and the average value was taken.

[0078] This experiment was conducted using the graduated cylinder method, and the specific procedures are as follows:

[0079] A 1000mL stoppered graduated cylinder (1mL accuracy) was used, with three parallel experiments per group (average value taken). 800mL of wastewater to be treated was poured into each graduated cylinder, with the water level approximately 35cm (the actual height of the graduated cylinder should be used as the reference). When sampling, water samples were taken from 10-15cm below the liquid surface (avoiding bottom sediment and surface scum). Then, an electric stirrer was used to stir rapidly at 200r / min for 2min to ensure that the flocculant and wastewater were fully mixed. Then, the stirring was slow at 80r / min for 10min to promote the slow coagulation of flocs. After stirring, the graduated cylinder was removed, gently placed on a horizontal experimental platform, and the timer was started. The cylinder was allowed to settle for 30min.

[0080] The following testing experiments were then conducted:

[0081] (1) Heavy metal ions (lead, zinc, cadmium, mercury): detected by atomic absorption spectrophotometry;

[0082] (2) Cyanide: Detected by isonicotinic acid-pyrazolone spectrophotometry;

[0083] (3) Ammonia nitrogen: Detected by Nessler's reagent spectrophotometry;

[0084] (4) Sulfides: Detected using the methylene blue spectrophotometric method;

[0085] (5) Humic acid and tannin: The absorbance was measured at wavelengths of 254 nm and 275 nm using ultraviolet spectrophotometry, and the content was calculated based on the standard curve.

[0086] (6) Water pH: Measured using a portable pH meter;

[0087] (7) Floc settling performance: After settling, the water body is divided into three layers from top to bottom: clear liquid, floc layer and dense sediment layer. At the initial moment (after stirring), the flocs are uniformly suspended without a clear interface. The corresponding graduated cylinder scale of the overall turbid system at this time is recorded as the initial total volume of flocs. After settling for 30 minutes, the boundary between the clear liquid and the floc layer is taken as the floc interface. The corresponding graduated cylinder scale is read to convert the settling distance and calculate the settling velocity (mm / min). At the same time, the total volume of the floc layer and the dense sediment layer is recorded. The volume compression ratio is calculated according to the formula (volume compression ratio = (initial floc volume - final floc volume) / initial floc volume × 100%) to quantify the density of flocs.

[0088] (8) Scum situation: After standing for 30 minutes, observe the amount of scum generated on the liquid surface through a graduated cylinder. Record the scum area as a percentage of the liquid surface area in the graduated cylinder into three levels: no scum, a small amount of scum (area < 1 / 3), and a large amount of scum (area ≥ 1 / 3).

[0089] The experimental results are shown in Table 1.

[0090] Table 1:

[0091]

[0092] Note: 1. “-” in Table 1 indicates that this item does not need to be tested; 2. The units of each indicator in Table 1 are as follows: lead, zinc, cadmium, mercury, cyanide, ammonia nitrogen, sulfide, humic acid, and tannin are all mg / L, pH has no unit, sedimentation velocity is mm / min, and volume compression ratio is .

[0093] As shown in Table 1, the composite flocculants prepared in Examples 1-2 can meet the basic water quality requirements for farmland irrigation and temporary miscellaneous water use after treatment, specifically: after treatment, the content of lead ≤0.015mg / L, zinc ≤0.042mg / L, cadmium ≤0.0010mg / L, and mercury ≤0.0004mg / L, which can reduce the content of various heavy metal ions in the water and reduce the risk of heavy metals seeping into the soil with irrigation water, affecting crop growth and human health; the cyanide content is ≤0.0032mg / L, which can improve the water quality. The system effectively intercepts cyanide complexes, improving their difficult-to-treat nature; ammonia nitrogen content ≤0.48mg / L helps reduce the interference of ammonium ions on floc settling and improves the stability of water ionic strength; sulfide content ≤0.0015mg / L reduces fine sulfide particle residue and lowers the probability of forming tannin-heavy metal-sulfide complex colloids; humic acid content ≤1.12mg / L and tannin content ≤0.92mg / L help dismantle heavy metal-humic acid complexes while reducing excessive tannin residue and the possibility of secondary colloid formation; the water pH is stabilized between 6.3 and 6.7, meeting the pH requirements for crop growth and temporary miscellaneous water use; floc settling speed ≥1.6mm / min, volume compression ratio ≥62%, and no scum is generated, enabling rapid floc settling and facilitating subsequent cleaning.

[0094] Example 3: Based on Example 1, potassium dihydrogen phosphate modified diatomaceous earth is added, and the treatment effect is better than that of Examples 1-2, making it more suitable for the treatment of various complex heavy metal wastewater in the Qinba Mountains of northern Sichuan.

[0095] Comparative Example 1: Due to the use of unmodified pectin and unmodified shellac, the pollutant removal effect was poor, the floc settling performance decreased, and a small amount of scum was easily generated, making it difficult to meet the treatment needs of regional complex polluted water bodies. Comparative Example 2: Due to the use of unmodified bentonite, the adsorption capacity for heavy metals and sulfides was insufficient, the floc nucleation effect was poor, the settling speed was slowed, and the volume compression ratio decreased, making it impossible to achieve good pollutant retention and rapid settling. Comparative Example 3: Due to the removal of cinnamyl xylan, the adsorption and fixation effect of hydrophobic benzene rings on sulfides and humic acids, as well as the particle cross-linking effect brought by double bonds, was lacking, resulting in poor tannin degradation, easy formation of secondary colloids, more pollutant residues, and flocs that easily loosened and floated. Comparative Example 4: Due to the use of unmodified pectinase, the lack of enzyme activity protection and dispersion regulation provided by trehalose composite modification resulted in easy aggregation and inactivation of the pectinase. This made it impossible to regulate the appropriate degradation of modified pectin, disrupting the hydrophilic-hydrophobic balance of the system and failing to alleviate the hydrophobic effect of cinnamylated xylan. Consequently, tannins could not be effectively adsorbed and settled, leading to increased scum production and decreased floc settling performance. Comparative Example 5: The removal of activated zeolite powder resulted in the lack of its porous adsorption and pH buffering effects, hindering the fixation of free galacturonic acid. This caused pH fluctuations in the water, and residual pollutants were difficult to fully adsorb, making it impossible to guarantee stable water quality compliance after treatment and unsuitable for weakly acidic, complexly polluted water bodies. Comparative Example 6: The removal of modified shellac resulted in poor retention of metal cyanide complexes, decreased floc aggregation capacity, and excessive residues of various pollutants, making it difficult to address the problem of difficult-to-treat metal cyanide complexes. Comparative Example 7 uses a conventional inorganic flocculant composition, which can only achieve simple adsorption and coagulation, resulting in the worst pollutant removal effect. The flocs have a slow settling speed, an extremely low volume compression ratio, and produce a large amount of scum, making it difficult to meet the water quality standards for farmland irrigation and temporary miscellaneous water use.

[0096] In addition, to further verify the suitability of the flocculant in Example 1 of this application for tannin-containing complex wastewater, an additional control experiment without tannin was set up (the concentration of other pollutants in the wastewater was the same as that in the raw water, the tannin content was ≤0.1mg / L, and all experiments were the same as above). The experimental results showed that the removal efficiency of heavy metals (lead, zinc, cadmium, mercury) in the control system was slightly improved, but the removal effect of cyanide was significantly weakened, and the floc settling performance deteriorated and a small amount of scum appeared. This is because the natural tannins in the wastewater can form hydrogen bonds with the hydroxyl groups of modified shellac, which helps the shellac to disperse evenly in weakly acidic water, so that the shellac molecules can fully coordinate and bind with the metal cyanide complex. At the same time, tannins can act as a bridge to promote the adsorption and retention of cinnamyl xylan, thereby improving the removal effect of metal cyanide complex. However, without the hydrogen bond interaction between tannins and the hydroxyl groups of shellac, the shellac is prone to agglomeration, which affects the synergistic flocculation with other components, resulting in uneven floc density and slowed settling speed. This result confirms that the composition design of the flocculant in this application is highly compatible with the scenario of complex polluted wastewater containing tannins.

[0097] It is worth noting that this application focuses on the removal of pollutants mentioned in complex heavy metal wastewater and does not involve the treatment verification of other indicators such as microorganisms. In practical applications, conventional disinfection and filtration processes can be combined with the wastewater source and water quality to meet the complete irrigation water standards.

Claims

1. A composite flocculant for the treatment of wastewater containing multiple heavy metals, characterized in that, It includes the following components by weight: 25-30 parts modified pectin, 18-22 parts modified shellac, 20-25 parts tartaric acid-bentonite complex, 10-15 parts cinnamicylated xylan, 5-10 parts galacturonic acid, 0.5-1 part trehalose-pectinase complex, and 2-3 parts activated zeolite powder; The modified pectin is obtained by modifying pectin with oxalic acid, and the carboxyl content of the modified pectin is 12%-15%. The modified shellac is obtained by modifying shellac with lactic acid; The cinnamic-acylated xylan is prepared by acylation of xylan with cinnamic anhydride, and the degree of substitution of the cinnamic-acylated xylan is 0.15-0.

20. The activated zeolite powder is made by activating natural zeolite with sodium bicarbonate solution.

2. The composite flocculant for the treatment of wastewater containing multiple heavy metals according to claim 1, characterized in that, The tartaric acid-bentonite composite has a particle size of 150-200 mesh, and the mass ratio of tartaric acid to bentonite is 1:(8-10).

3. The composite flocculant for the treatment of wastewater containing multiple heavy metals according to claim 1, characterized in that, In the trehalose-pectinase complex, the mass ratio of trehalose to pectinase is (15-20):(80-85).

4. The composite flocculant for the treatment of wastewater containing multiple heavy metals according to claim 1, characterized in that, The activated zeolite powder has a particle size of 200-300 mesh; the sodium bicarbonate solution has a mass fraction of 4-8%; and the solid-liquid ratio of zeolite to sodium bicarbonate solution is 1:(5-10), g:ml.

5. The composite flocculant for treating wastewater containing multiple heavy metals according to claim 1, characterized in that, In the cinnamic acylated xylan, the mass ratio of xylan to cinnamic anhydride is 1:(0.3-0.5).

6. The composite flocculant for treating wastewater containing multiple heavy metals according to claim 1, characterized in that, In the modified pectin, the mass ratio of oxalic acid to pectin is 1:(12-15).

7. The composite flocculant for the treatment of wastewater containing multiple heavy metals according to claim 1, characterized in that, In the modified shellac, the mass ratio of lactic acid to shellac is 1:(10-15).

8. A method for preparing the composite flocculant according to any one of claims 1 to 7, characterized by, Includes the following steps: S1. Take the tartaric acid-bentonite complex, add deionized water and stir to make a suspension; S2. Mix the modified pectin and modified shellac, add them to the suspension, heat to 40-45℃ and stir at a constant temperature. After stirring, cool to room temperature, add cinnamicyl xylan, galacturonic acid, trehalose-pectinase complex, and activated zeolite powder in sequence, stir thoroughly, and then dry and pulverize under vacuum at low temperature to obtain the flocculant.

9. The method for preparing the composite flocculant according to claim 8, characterized in that, In step S2, the vacuum low-temperature drying temperature is <40℃.

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