CN115417626A - Method for solidifying/stabilizing landfill leachate concentrated solution by using geopolymer - Google Patents

Abstract

The invention discloses a method for treating landfill leachate concentrated solution by utilizing geopolymer solidification/stabilization. The formed raw stock is naturally placed after injection molding, maintenance and demolding, and then the solidification/stabilization of the landfill leachate concentrated solution pollutants is completed. The added solid alkali activator obviously improves the liquid-solid ratio of the geopolymer and increases the disposal quantity of the landfill leachate concentrated solution. The geopolymer precursor is a byproduct such as slag, fly ash and red mud which are produced in large quantity in industrial production, and is cheap and easy to obtain. The method has excellent solidification/stabilization capability on organic matters, ammonia nitrogen, inorganic salts and heavy metals in the landfill leachate concentrated solution, realizes high-efficiency, low-cost and zero-emission treatment of the landfill leachate concentrated solution and resource utilization of industrial solid wastes, and has good popularization and application prospects.

Description

A method for solidifying/stabilizing landfill leachate concentrate using geopolymer method

technical field

The invention relates to solidification/stabilization treatment of high-salt organic wastewater. Specifically, the invention uses geopolymer as a solidification agent to realize efficient and harmless treatment of landfill leachate concentrate.

Background technique

Landfill leachate is a kind of high-concentration organic wastewater that is inevitably produced in the process of landfill or stockpiling. In the past few decades, with the maturity of membrane bioreactor technology, large-scale treatment of landfill leachate has been realized. This "biochemical method + membrane treatment" technology has a satisfactory treatment effect and stable water quality, and has been implemented in many countries such as China. However, due to the limitations of membrane technology, especially the lack of high-efficiency fouling-resistant membranes, the membrane concentrate, which accounts for about 1/3 of the leachate volume, will be produced during the treatment process, forming landfill leachate concentrate. Landfill leachate concentrate contains a large amount of organic matter, ammonia nitrogen, inorganic salts and heavy metals. The composition is complex and difficult to degrade, which has become a major problem in industrial wastewater treatment.

The existing landfill leachate concentrate treatment methods mainly include recharge, evaporation, incineration, membrane distillation and advanced oxidation treatment. Recharge will cause the accumulation of organic matter and salt, which will reduce the activity of microorganisms and affect the stability of subsequent membrane treatment. Evaporation and incineration can reduce the concentrate by more than 90%, but the high concentration of chloride ions in the concentrate is extremely corrosive. Membrane distillation has problems such as high cost of membrane preparation, low thermal conductivity and low membrane flux, which limit its large-scale use. Advanced oxidation treatment is also strongly restricted due to economic cost reasons. Therefore, it is urgent to develop high-efficiency, low-cost and green landfill leachate concentrate treatment technology.

Solidification/stabilization uses physical or chemical methods to fix or contain hazardous waste in landfill leachate concentrate in an inert solid matrix, so that it presents chemical stability or sealing, low cost, good effect, and realizes the non-toxicity of hazardous waste. Harmful treatment has important application prospects. Patent CN 103910481 B discloses a kind of solidification/stabilization of landfill leachate or landfill leachate membrane concentrate by using a covalent bond type inorganic-organic composite flocculant and Portland cement to compound the sludge, which has good organic matter and Heavy metal solidification ability. Patent CN 111995111 A achieves harmless and stable disposal of landfill leachate concentrate by stepwise separating heavy metals in landfill leachate concentrate, and then adding sodium sulfate/calcium and Portland cement to solidify/stabilize it. However, cement's high carbon emissions and resource consumption make its development unsustainable. In addition, the defects of large volume expansion, insufficient durability, and susceptibility to carbonization and corrosion in the curing process of cement make its large-scale application controversial.

In recent years, as a new type of inorganic solidified material, geopolymer has the advantages of simple preparation process, excellent mechanical properties and low energy consumption. Under normal temperature and pressure, mix and react water glass, sodium hydroxide, aluminum source (fly ash, slag and tailings), and obtain it after short-term (2-24h) curing. It has fire resistance, high temperature resistance and chemical corrosion resistance. The advantages. It is reported that the energy consumption of geopolymer is 60% of Portland cement, and has lower _CO2 emission, which is only 10%-20% of Portland cement. Based on this, the present invention adopts geopolymer solidification/stabilization technology to realize low-cost, high-efficiency and harmless treatment of landfill leachate concentrate, and realizes various pollutions such as organic matters, inorganic salts, ammonia nitrogen and heavy metals in landfill leachate concentrate Simultaneous curing/stabilization of substances.

Contents of the invention

The present invention aims to provide a method for efficiently synchronously solidifying/stabilizing organic matters, inorganic salts, ammonia nitrogen and heavy metals in the landfill leachate concentrate by using geopolymers. The specific steps are as follows:

Step 1, solid alkali activator, landfill leachate concentrate and geopolymer precursor are added to the mixer successively after metering, the mass ratio of each component is: solid alkali activator 15% ~ 25%, landfill leachate concentrated Liquid 25% to 50%, geopolymer precursor 35% to 60%. Since the landfill leachate concentrate contains a large amount of water, the entire solidification/stabilization system does not need to add any additional reagent water.

Step 2. Turn on the agitator to stir, so that the materials are evenly mixed to form a slurry that can be poured into the mold.

Step 3. Inject the slurry into the forming mold, and shake it for 30 to 60 seconds on the shaking table to discharge the air bubbles in the slurry to form a solidified block with regular shape.

Step 4. Seal the solidified block and place it in a high-temperature box for curing at a temperature of 60° C. to 90° C. for 18 to 36 hours. After curing, take it out of the high-temperature box, keep it in a natural state for 3 to 28 days, complete the curing/stabilization treatment, and test various indicators.

Further, the solid alkali activator in step 1 is a mixture of sodium silicate powder and sodium hydroxide particles prepared in proportion, and the modulus of the mixed activator is 0.89-1.16.

Further, the geopolymer precursor in step 1 is one or more compositions of blast furnace slag, steel slag, fly ash, red mud and metakaolin, and its characteristics are that the active _SiO2 content is 30% to 60%, the active Al The content of ₂ O ₃ is 15%-45%, the content of active CaO is 0%-45%, and the total content of other Fe ₂ O ₃ , NaO and K ₂ O is 5%-20%.

Further, the stirring time in step 2 is 5-10 minutes, the initial setting time is used to determine the amount of landfill leachate concentrate added, the lower limit of the initial setting time is 10-30 minutes, and the upper limit is 80-100 minutes.

During the solidification/stabilization process of the geopolymer of the present invention, the humic acid in the landfill leachate concentrate forms sodium humate/calcium precipitates with calcium ions and sodium ions under strong alkaline conditions and fills the gaps of the geopolymer And in micropores, ammonia nitrogen is stabilized by zeolite-like hydration gel in geopolymers, chloride ions are stabilized by forming Fischer salts under alkaline excitation conditions, and sulfate ions are stabilized by forming calcium sulfate/sodium crystals. The dense hydrated calcium/sodium aluminosilicate and hydrated calcium/sodium silicate gel structure of geopolymer have excellent physical sealing effect on the pollutants of landfill leachate concentrate.

Advantage and beneficial effect that the present invention obtains are:

(1) The present invention uses common industrial by-products (blast furnace slag and fly ash, etc.) as the main solidification/stabilization material, which has a wide range of sources and low cost, avoids the use of cement and other non-renewable resources with large energy consumption and carbon emissions, and can Save a lot of treatment costs of landfill leachate concentrate while reducing resource consumption and carbon emissions;

(2) The present invention adopts a solid alkali activator, which greatly improves the processing capacity of the geopolymer to the liquid landfill leachate concentrate, and reduces the risk of transportation and use;

(3) The present invention adopts solid alkali activator, landfill leachate concentrate and geopolymer precursor to add at one time, solves the conventional geopolymer preparation process and needs to prepare the stepwise addition of alkali activator solution in advance, and simplifies the process flow, Improve the feasibility of industrial application;

(4) The present invention can well reduce the pollutant toxicity of the landfill leachate concentrate, reduce environmental risks, and simultaneously not discharge waste, and realize zero discharge treatment of the landfill leachate concentrate;

(5) The solidified/stabilized geopolymer solidified block obtained by the present invention has good compressive strength and hydraulic property, and can be used as brick making and roadbed material because it has no risk of environmental pollution.

Description of drawings

Fig. 1 is a schematic flow chart of the geopolymer solidification/stabilization landfill leachate concentrate of the present invention.

Figure 2 is the optical photograph and scanning electron micrograph of the prepared geopolymer solidified block.

Figure 3 shows the effect of alkali activator modulus on the compressive strength of geopolymer solidified block.

Figure 4 shows the effect of landfill leachate concentrate content on the compressive strength of geopolymer solidified blocks.

detailed description

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Example 1:

In this example, the nanofiltration membrane concentrate of landfill leachate from a waste landfill in Tianjin was treated. The contents of organic matter, ammonia nitrogen, inorganic salts and heavy metals are shown in Table 1. The COD _Cr concentration of the landfill leachate concentrate is 3873.6mg L ^-1 , and the ammonia nitrogen concentration is 72.4mg ^-1 , both of which are higher than the "Pollution Control Standards for Domestic Waste Landfill Sites" (GB 16889—2008), and further treatment is required to meet the discharge standards . In addition, the landfill leachate concentrate sample also contained a large amount of inorganic salts (TDS=89.3g L ^-1 ) and a small amount of heavy metals, which had potential ecological risks.

The landfill leachate concentrate solidification/stabilization method of the present embodiment comprises the following steps (Fig. 1):

Step 1. Take 242 mL of the landfill leachate concentrate and put it into a blender, add 50 g of sodium hydroxide particles and 120 g of sodium silicate powder into the blender, and stir to make the materials evenly mixed. Next, 300 g of ground blast furnace slag were added to the mixer.

Step 2. Turn on the agitator and stir for 5 minutes to mix the materials evenly and form a slurry that can be poured into the mold.

Step 3. Inject the slurry into the forming mold, shake it on the shaking table for 60 seconds, discharge the air bubbles in the slurry, and form solidified blocks with regular shapes.

Step 4. Seal the cured block and place it in a high-temperature box for curing at a temperature of 70°C for 24 hours. After curing, take it out of the high-temperature box and keep it in a natural state for 24 days.

As shown in Figure 2, the obtained geopolymer solidified block has good structural strength and hydraulicity, and its 28-day unconfined compressive strength can reach 7Mpa. X-ray diffraction and scanning electron microscopy showed that the solidified mass formed produced large amounts of hydrated calcium/sodium silicate and hydrated calcium/sodium aluminosilicate gels, as well as other stabilizing components such as Fischer's salt and calcium sulfate (Fig. 2c and 2d). According to "Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillating Method" (HJ 557-2010), the above-mentioned solidified/stabilized samples were pulverized and the leachate was obtained. The concentrations of organic matter, ammonia nitrogen, inorganic salts and heavy metals were detected in Table 2. Landfill Pollution Control Standards (GB 16889-2008) and Integrated Sewage Discharge Standards (GB 8978-1996).

Table 1. Detection index concentration of landfill leachate concentrate

N.D. means that the concentration of the detection index is lower than the detection limit of the instrument.

Table 2. Pollutant leaching concentration of slag-based geopolymer solidification/stabilization landfill leachate concentrate

N.D. means that the concentration of the detection index is lower than the detection limit of the instrument, / means that the index has not been clearly required in the standard.

Example 2:

The landfill leachate concentrate source and the solidification/stabilization method of this implementation process are all the same as in Example 1, except that:

The geopolymer precursor in step 1 is fly ash.

In step 1, add 300 g of fly ash, 120 g of sodium silicate powder, 50 g of sodium hydroxide, and 200 mL of landfill leachate concentrate.

The curing temperature of the geopolymer solidified block in step 4 is 80°C.

The 28-day unconfined compressive strength of the fly ash-based geopolymer solidified block obtained in this example is 11 Mpa. According to "Solid Waste Leaching Toxic Leaching Method Horizontal Oscillating Method" (HJ 557-2010), the above-mentioned solidified/stabilized samples were pulverized and the leachate was obtained. The concentrations of organic matter, ammonia nitrogen, inorganic salts and heavy metals were detected in Table 3. Landfill Pollution Control Standards (GB 16889-2008) and Integrated Sewage Discharge Standards (GB 8978-1996).

Table 3. Pollutant leaching concentration of fly ash-based geopolymer solidified/stabilized landfill leachate concentrate

N.D. means that the concentration of the detection index is lower than the detection limit of the instrument, / means that the index has not been clearly required in the standard.

Example 3:

In order to further investigate the influence of the alkali activator modulus in step 1 on the compressive strength of the prepared geopolymer solidified block, by adjusting the ratio of sodium hydroxide particles and sodium silicate powder, the activator modulus of 0.89-1.27 was obtained. Solid base activator, other curing/stabilization processes are the same as in Example 2, and the results are shown in Figure 3.

The unconfined compressive strength of geopolymer solidified blocks at 3, 7, 14 and 28 days were measured under different alkali activator moduli. As the curing time prolongs, the compressive strength of the prepared geopolymer solidified block increases continuously, which is attributed to the continuous occurrence of geopolymerization reaction, forming a denser and stronger geopolymer gel. As the modulus of the alkali activator increased from 0.89 to 1.16, the 28-day compressive strength of the prepared geopolymer cured block increased continuously. However, when the alkali activator modulus was further increased to 1.27, the 28-day compressive strength of the prepared geopolymer cured block decreased instead. Stronger alkali content is beneficial to the dissolution and repolymerization of active silica-alumina in fly ash, while too high alkali concentration will intensify the ion-pair effect of Na ⁺ and OH ^- and reduce the alkali activity.

Example 4:

In order to further investigate the impact of the content of the landfill leachate concentrate on the compressive strength of the prepared geopolymer solidified block in step 1, by adjusting the addition of the landfill leachate concentrate, the liquid-solid ratios of 0.50, 0.55, 0.59 and 0.64 geopolymer solidification/stabilization system, other solidification/stabilization processes are the same as in Example 2, and the results are shown in Figure 4.

The unconfined compressive strength of geopolymer solidified blocks at 3, 7, 14 and 28 days were measured under different liquid-solid ratio conditions. With the increase of the liquid-solid ratio, the 28-day compressive strength of the formed geopolymer solidified blocks continued to decrease, indicating that the content of landfill leachate concentrate is a key factor affecting the compressive properties of geopolymers. The landfill leachate concentrate, as the only solvent in the geopolymer, provides a solution environment for the reaction of active silica-alumina. Excessively high solvent will dilute the alkali concentration of the system and reduce the dissolution rate of active silica-alumina. In this embodiment, due to the use of the solid alkali activator, the treatment capacity of the landfill leachate concentrate of the geopolymer is greatly improved, and the liquid-solid ratio is obviously higher than that of the traditional geopolymer (0.15-0.30). In addition, the content of landfill leachate concentrate will also significantly affect the initial setting time of geopolymers, which should be considered in practical engineering applications.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (4)

1. A method utilizing geopolymer efficient synchronous solidification/stabilization of organic matter, inorganic salts, ammonia nitrogen and heavy metals in the landfill leachate concentrate, is characterized in that, the method comprises the following steps: Step 1, solid alkali activator, landfill leachate concentrate and geopolymer precursor are added to the mixer successively after metering, the mass ratio of each component is: solid alkali activator 15% ~ 25%, landfill leachate concentrated Liquid 25% to 50%, geopolymer precursor 35% to 60%. Step 2. Turn on the agitator to stir, so that the materials are evenly mixed to form a slurry that can be poured into the mold. Step 3. Inject the slurry into the forming mold, and shake it for 30 to 60 seconds on the shaking table to discharge the air bubbles in the slurry to form a solidified block with regular shape. Step 4. Seal the solidified block and place it in a high-temperature box for curing at a temperature of 60-90° C. for 18-36 hours. After curing, take it out of the high-temperature box, keep it in a natural state for 3 to 28 days, complete the curing/stabilization treatment, and test various indicators. 2. according to the described landfill leachate concentrate solidification/stabilization method of claim 1, it is characterized in that, in step 1, solid alkali activator is the mixture that sodium silicate powder and sodium hydroxide particle are prepared in proportion, and the activation after mixing The modulus of the agent is 0.89-1.16. 3. according to the described landfill leachate concentrate solidification/stabilization method of claim 1, it is characterized in that, in step 1, geopolymer precursor is a kind of or of blast furnace slag, steel slag, fly ash, red mud and metakaolin A variety of compositions, characterized by active SiO ₂ content of 30% to 60%, active Al ₂ O ₃ content of 15% to 45%, active CaO content of 0% to 45%, other Fe ₂ O ₃ , NaO and K The total content of ₂ O and the like is 5% to 20%. 4. according to the described landfill leachate concentrate solidification/stabilization method of claim 1, it is characterized in that, in step 2, stirring time is 5～10min, adopt initial setting time to judge the addition of landfill leachate concentrate, initial setting time The lower limit is 10 to 30 minutes, and the upper limit is 80 to 100 minutes.

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