CN112898978B

CN112898978B - Repairing agent for lead-polluted alkaline soil and preparation and use methods thereof

Info

Publication number: CN112898978B
Application number: CN202110037216.5A
Authority: CN
Inventors: 梁田; 杨宾; 李发生
Original assignee: Chinese Research Academy of Environmental Sciences
Current assignee: Chinese Research Academy of Environmental Sciences
Priority date: 2021-01-12
Filing date: 2021-01-12
Publication date: 2021-11-16
Anticipated expiration: 2041-01-12
Also published as: CN112898978A

Abstract

The invention relates to a lead-contaminated soil remediation agent and a preparation and use method thereof. The invention provides a lead-polluted soil remediation method for adjusting the form of heavy metal and dissolving out phosphate radical by using acidic biomass charcoal. The repairing agent comprises 7.5-45 wt% of acidic biomass charcoal and 55-92.5 wt% of apatite. The preparation method comprises the following steps: (1) drying and crushing; (2) carbonizing at low temperature; (3) cooling and sieving; (4) mixing and stirring. When in use, the repairing agent and soil are mixed according to the lead-phosphorus molar ratio of 1: 5-1: 10, mixing; then mixing with soil for moisture preservation and maintenance. The method has the advantages of simple raw materials, mature preparation process, no secondary pollution and capability of improving the content of the phosphorus-chlorine-lead ore products with stronger stability in the soil, thereby realizing the long-term safety and the low cost of disposal of the repaired lead-polluted soil.

Description

Repairing agent for lead-polluted alkaline soil and preparation and use methods thereof

Technical Field

The invention relates to the field of heavy metal contaminated soil remediation in ecological environment protection, and particularly relates to a lead contaminated soil remediation agent and a preparation and use method thereof.

Technical Field

Lead is one of the heavily regulated pollutants in soil. The frequency of lead in heavy metal contaminated sites which are treated preferentially in the United states is 15%, and the proportion of lead content in Japanese contaminated sites which exceeds the environmental quality standard is 43%. The problem of lead pollution of the soil in China is also severe, and the exceeding rate of the pollution point of the lead in the soil is 1.5 percent as pointed out in national soil pollution condition survey bulletin issued in 2014. Lead in the environment cannot be biodegraded and its toxicity and cumulative nature can create a variety of direct and indirect hazards to the ecosystem and human health.

The strategies for repairing lead-contaminated soil are mainly two: firstly, the total amount of lead in soil is reduced by means of chemical leaching, electric restoration, plant restoration and the like; and secondly, the biological effectiveness and the mobility of the lead in the environment are reduced by changing the combination mode or occurrence form of the lead and the soil, so that the risk control is realized. Based on the research progress at home and abroad and the practice of engineering cases, the risk control technology represented by solidification and stabilization is the most commonly used restoration strategy for restoring lead-polluted soil.

Phosphate is the most commonly used restoration material in lead polluted soil solidification and stabilization, especially natural apatite, and has wide application in restoration practice due to the characteristics of large reserve, low cost and the like. By adding phosphate materials into the soil, the phosphate is promoted to react with lead in the soil to generate insoluble phosphorus-lead chloride ore: pb5(PO4)3X (X = OH, F, Cl), is the primary mechanism that reduces lead migration in contaminated soils. For example, CN 107384417B discloses a phosphorus slag-based repair material for lead-contaminated soil, which is prepared by mixing phosphorus slag, a certain proportion of slag, petroleum coke desulfurized ash and cement kiln ash. CN 111205872 a discloses a stabilizing compound medicament for lead-contaminated soil and a use method thereof, wherein the compound medicament also contains phosphate radical. However, the repairing material in the invention does not greatly increase the content of the core products of lead phosphate minerals and phosphorus-lead chloride ores while improving the lead pollution repairing effect, and the long-term safety after soil repairing cannot be guaranteed. The phenomenon is more obvious when alkaline repair materials such as cement kiln dust and the like are added or polluted soil with alkaline pH is repaired.

In order to overcome the defect, CN 110871213 a discloses a method for stabilizing/solidifying lead-contaminated soil, which is characterized in that ferrous sulfate solution is added into the lead-contaminated soil, and Fe is added into the lead-contaminated soil²⁺By oxidation of⁺Promoting the transformation of unstable lead in soil to an effective state; and adding the biomass charcoal and the phosphate into the lead-polluted soil again to restore the polluted soil. The content of a repaired stable product is increased, the long-term stability of the repaired soil is improved, but the additionally provided ferrous sulfate solution is easy to pollute the environment, sulfate radicals are easy to corrode buildings, iron ions do not belong to pollution elements which are mainly monitored in the soil and underground water, but are easy to discolor water bodies, visual discomfort and gustatory discomfort are caused, and the defects limit the application of the repairing agent in the repairing of the lead-polluted soil.

The phosphate is an effective restoration technology, and is recommended by the U.S. EPA as one of the priority treatment methods of the lead-polluted soil, but the problems of the safety of restoration materials, the long-term stability of the restored lead-polluted soil, the cheapness of treatment after the restoration of the lead-polluted soil, the economy of restoration implementation and the like still exist.

Disclosure of Invention

In order to solve the problems that the long-term stability is poor after the heavy metal lead pollution is repaired, and the treatment of the repaired polluted soil is further influenced due to the fact that a repairing agent brings secondary pollution in the prior art, the invention provides a method for repairing the lead polluted soil by using acidic biomass carbon to adjust the form of the heavy metal and dissolve out phosphate radicals, the content of stable lead products in the soil is increased, and therefore the long-term safety and the treatment cheapness of the repaired lead polluted soil are achieved.

The purpose of the invention is realized by the following technical scheme:

a restoration agent for lead-polluted alkaline soil comprises 7.5-45 wt% of acidic biomass charcoal and 55-92.5 wt% of apatite; the pH of the acidic biomass charcoal is less than 6.5; the apatite is fluorapatite widely existing in nature.

The preparation method of the remediation agent for the lead-polluted alkaline soil comprises the following steps:

(1) drying and crushing: drying the biomass raw material at 100-110 ℃ to constant weight, mechanically crushing and coarsely screening;

(2) low-temperature carbonization: placing the biomass raw material obtained in the step (1) in a quartz boat of a tubular furnace, introducing inert gas at a rate of 0.5-1L/min, heating the tubular furnace at a rate of 5-10 ℃/min, firing at a temperature of 250-450 ℃, and keeping the temperature for 2-5 h;

(3) cooling and sieving: naturally cooling the biomass charcoal obtained in the step (2), taking out, grinding and sieving to obtain acidic biomass charcoal;

(4) mixing and stirring: grinding apatite, and sieving; mixing 7.5-45 wt% of acidic biomass carbon and 55-92.5 wt% of apatite, and stirring to be uniform.

Preferably, the biomass raw material in the step (1) is willow branches and pine branches with high lignin content.

Preferably, the inert gas introduced in the step (2) is nitrogen and/or carbon dioxide, and the inert gas is introduced at a rate of 0.6L/min.

Preferably, the temperature rise rate of the tubular furnace in the step (2) is 5 ℃/min, the burning temperature of the biomass charcoal is 300 ℃, and the temperature is kept for 2 h.

A method for repairing lead-contaminated alkaline soil by using the repairing agent comprises the following steps: firstly, mixing a repairing agent and soil according to a lead-phosphorus molar ratio of 1: 5-1: 10, mixing; and secondly, keeping the water content of the mixed soil between 30% and 50%, fully and uniformly stirring, and maintaining.

Compared with the prior art, the invention has the beneficial effects that:

according to the invention, an acidic slow-release microenvironment is provided by the acidic biomass charcoal, so that unstable lead, especially weak acid extractable lead in soil can be durably and slowly promoted to be converted into water-soluble lead ions, the reaction activity of the lead ions in the soil is improved, the micro-interface reaction of the lead ions and apatite is promoted, the content of a core repair product, namely the lead-phosphorus-chloride ore, is improved, and the long-term safety after repair is enhanced.

The invention provides an acidic slow-release microenvironment through the acidic biomass charcoal, can persistently and slowly promote apatite dissolution to release phosphate radicals and halogen anions, and the phosphate radicals and the halogen anions can rapidly generate the phosphorus-chlorine-lead ore with stable geochemical properties with lead ions, thereby greatly improving the utilization efficiency of phosphorus in the repair material, reducing the usage amount of phosphate, and avoiding secondary pollution such as eutrophication and the like to a water body.

The method has the advantages that the used acidic biomass charcoal is low in firing condition temperature and high in yield of 35-45%, the used raw materials can use forestry and wood processing industry wastes, the wastes are recycled, and the method is economical and energy-saving.

The apatite used in the invention is natural phosphate mineral, is widely distributed in the nature, does not need secondary processing, and the acidic biomass charcoal promotes the dissolution and release of the apatite, thereby overcoming the defects of poor solubility and poor repairing effect.

The invention has the advantages of simple raw materials, mature preparation process, no need of deep processing, no introduction of raw materials which can corrode buildings or pollute underground water, lasting repairing effect after the medicament is put into the device, high content of core products after repairing, good stability and high safety. The repaired soil can be comprehensively utilized as roadbed, greening underground filling and the like, and the problem that the repaired lead polluted soil is difficult to dispose is solved.

Description of the drawings:

FIG. 1 XRD representation of apatite and lead hydroxide reaction under the action of acidic biomass charcoal

FIG. 2 XRD characterization of apatite and lead carbonate reaction under acidic biomass charcoal action

Detailed Description

The technical solution of the present invention is further clearly and completely described below by way of examples, which are a part of the examples of the present invention, but not all of the examples. All technical solutions obtained by a person skilled in the art without creative efforts based on the embodiments of the present invention belong to the protection scope of the present invention.

The invention provides a repairing agent for lead-polluted alkaline soil and a preparation method and a use method thereof.

The inventor dries the sawdust of pine trees and poplar trees at 110 ℃ to constant weight, respectively introduces nitrogen into a tube furnace at the speed of 0.6L/min, respectively heats the sawdust to 300 ℃ and 400 ℃ at the heating rate of 5 ℃/min, then preserves the temperature for two hours, cools the sawdust to room temperature, takes biomass charcoal, grinds the biomass charcoal and sieves a 100-mesh sieve for later use. The following table was used to measure the pH of the acidic biomass char:

	300℃	400℃
			pine biomass charcoal	5.86	6.95
Poplar biomass charcoal	4.92	6.33

Grinding natural apatite, and sieving with 100 mesh sieve.

According to the mass ratio of the acidic biomass charcoal to the apatite of 1: 6.25 preparing composite repairing agent, respectively marked as S300, S400, Y300, Y400 (S stands for pine, Y stands for poplar, 300, 400 stands for firing temperature), mixing uniformly, and packaging for later use.

Example 1

The research shows that lead carbonate, basic lead carbonate and lead hydroxide widely exist in a target range and a lead-zinc tailing pond pollution area and are main components of unstable lead. In order to more intuitively embody the gain effect of the present invention, a remediation agent is employed to react directly with typical contaminants. The specific comparative experimental protocol is as follows:

experiment group one: s3007.25g and 0.322g of lead carbonate are put into a 50mL centrifuge tube, 20mL of deionized water is added, and then the centrifuge tube is placed into a constant temperature reciprocating type shaking table to be oscillated for 24 hours at the rotating speed of 160 rpm and the temperature of 25 ℃. Centrifuging the mixture at 4000 g for 10 min, freeze drying the solid substance at the lower layer, grinding, and sieving with 200 mesh sieve.

Experiment group two: s4007.25g, lead carbonate 0.322g and other steps are the same as those of experiment group one.

Experiment group three: y3007.25g, lead carbonate 0.322g, and other steps are the same as the experimental group I.

Experiment group four: y4007.25g, lead carbonate 0.322g, and the other steps are the same as those of experiment group one.

Experiment group five: s3007.25g, 0.291g of lead hydroxide and other steps are the same as those in the first experimental group.

Experiment group six: s4007.25g, lead hydroxide 0.291g, and other steps are the same as those in experiment group one.

Experimental group seven: y3007.25g, lead hydroxide 0.291g, and other steps are the same as those in experiment group one.

Experiment group eight: y4007.25g, lead hydroxide 0.291g, and other steps are the same as those of experiment group one.

Control group one: 6.25g of apatite and 0.322g of lead carbonate, and the other steps are the same as those of experiment group one.

Control group two: 6.25g of apatite and 0.291g of lead hydroxide, and the other steps are the same as those of experiment group one.

Taking a sample to be tested to test the components and the structure of a reaction product, wherein the test instrument adopts an X-ray diffractometer (XRD), and the test result is shown in the specification, namely figure 1 and figure 2.

Comparing the XRD material standard pattern, under the condition of defining all reaction products and possible products, when the 2 theta is 30 degrees, the lead-phosphorus-chloride ore indicating peak which is the expected core product of the invention can be considered, because the testing conditions are consistent, the intensity of the indicating peak can be semi-quantitatively determined the content of the product, and the half width and the height of the indicating peak can indicate the crystallization degree of the product.

Compared with a control group, the test result shows that the content and the crystallization degree of the phosphorus-chlorine-lead ore which is a core product of the experimental group are obviously improved, the key effect of the acidic biomass charcoal in the invention is shown, the result in the experimental group shows that the poplar biomass charcoal has a larger gain effect than the pine biomass charcoal, and the same biomass charcoal raw material is selected, so that a lower pH value caused by a lower firing temperature can provide a larger gain effect for repairing. The result has important significance for long-term safety of the repaired contaminated soil and treatment of the repaired contaminated soil.

Example 2

A lead-contaminated soil remediation agent is recorded as follows by mass percent: 28.5 percent of poplar biomass charcoal prepared at 300 ℃ of 100 meshes and 71.5 percent of apatite prepared at 100 meshes, and the preparation method is as described above.

Taking lead polluted soil of a certain lead storage battery retired site, testing that the total lead concentration is 2567mg/kg, and testing the heavy metal form by adopting a BCR distribution extraction method, wherein the content of the weak acid extractable state accounts for 48.2%, and the content of the residue state accounts for 11.7%. 200g of contaminated soil and 35g of remediation agent (the mass ratio of biomass carbon to soil is 1: 20, and the molar ratio of lead to phosphorus is 1: 10) are taken and uniformly stirred in a 1L polypropylene box, 75mL of deionized water is added to enable the water content of the soil to be 35%, the soil is placed in a thermostat for maintenance for 7 days, freeze drying is carried out after maintenance is finished, and 3 parallel samples are set in an experiment. The dried sample was tested to have a lead leaching concentration of 0.0079mg/L according to the sulfuric acid-nitric acid method (HJ 299-2007) for leaching toxicity of solid wastes.

The invention shows that the preparation of the composite remediation agent of the acidic biomass charcoal and phosphate embodies the design idea of regulation and control and then remediation, and the acidic biomass charcoal provides a long-term slow-release acidic microenvironment to promote the conversion of unstable-state lead into water-soluble-state lead with higher reaction activity and insoluble apatite to release phosphate radicals, so that the content and the crystallinity of a reaction core product, namely the phosphorus-chlorine-lead ore, are increased, and the long-term safety of the remediated soil is improved.

The repairing agent does not introduce polluting substances and cannot hinder the treatment of the repaired polluted soil.

Claims

1. A restoration agent for lead-polluted alkaline soil, which is characterized in that: the material consists of 7.5 to 45 weight percent of acidic biomass charcoal and 55 to 92.5 weight percent of apatite; the pH of the acidic biomass charcoal is less than 6.5; the apatite is fluorapatite; the raw material of the acidic biomass charcoal is willow branches with high lignin content; the firing temperature of the acidic biomass charcoal is 300 ℃.

2. A method for preparing the repairing agent according to claim 1, comprising the steps of:

(2) low-temperature carbonization: placing the biomass raw material obtained in the step (1) in a quartz boat of a tubular furnace, introducing inert gas at a rate of 0.5-1L/min, heating the tubular furnace at a rate of 5-10 ℃/min, firing at 300 ℃, and keeping the temperature for 2-5 h;

3. The method for producing a repair agent according to claim 2, characterized in that: the inert gas introduced in the step (2) is nitrogen and/or carbon dioxide, and the velocity of introducing the inert gas is 0.6L/min.

4. The method for producing a repair agent according to claim 2 or 3, characterized in that: and (3) in the step (2), the temperature rising rate of the tubular furnace is 5 ℃/min, the burning temperature of the biomass charcoal is 300 ℃, and the temperature is kept for 2 h.

5. A method of using the repair agent of claim 1: firstly, mixing a repairing agent and soil according to a lead-phosphorus molar ratio of 1: 5-1: 10, mixing; and secondly, keeping the water content of the mixed soil between 30% and 50%, fully and uniformly stirring, and maintaining.