1. A method for treating and recycling heavy metal contaminated soil leaching waste liquid is characterized by comprising the following steps:

(1) treating Pb, Cu and Zn heavy metal composite polluted soil by using a soil eluting agent, carrying out solid-liquid separation, and collecting soil eluting waste liquid containing Pb, Cu and Zn ions;

(2) introducing H into the leaching waste liquid₂S gas makes heavy metal step sulfurize, the step sulfurizing of the heavy metal is through adjusting H₂S is introduced into the waste liquid system by controlling H₂Partial pressure of S to control H₂S, the volume of the solution is increased, the step vulcanization of heavy metal is realized according to the difference of heavy metal Ksp, so that the solution sequentially generates CuS, PbS and ZnS, and the heavy metal sulfide precipitate is generated by step-by-step solid-liquid separation and recovery, so that the leaching waste liquid is regenerated into the soil leaching agent;

(3) and (4) treating the heavy metal contaminated soil by recycling the regenerated soil eluting agent.

2. The method for treating and recycling the heavy metal contaminated soil leaching waste liquid according to claim 1, which is characterized in that: the eluent is inorganic strong acid solution such as dilute nitric acid and dilute sulphuric acid or organic acid solution such as EDTA and citric acid, and the concentration is 0.25-1 mol/L.

3. The method for treating and recycling the heavy metal contaminated soil leaching waste liquid according to claim 1 or 2, which is characterized in that: said H₂The volume of the S introduced into the waste liquid system is 3-25 mmol/L.

4. The method for treating and recycling the heavy metal contaminated soil leaching waste liquid according to claim 3, which is characterized in that: the adjustment H₂The partial pressure method for introducing S into the waste liquid system comprises the following specific steps: introducing H with the volume of 3-4mmol/L into the leaching waste liquid₂S gas reacts for 5-15min and then is subjected to solid-liquid separation; then introducing H with the volume of 1-2mmol/L into the residual liquid₂S gas reacts for 5-15min and then is subjected to solid-liquid separation; then introducing H with the volume of 12-20mmol/L into the residual liquid₂And (5) reacting S gas for 5-15min, and then carrying out solid-liquid separation.

5. The method for treating and recycling the heavy metal contaminated soil leaching waste liquid according to claim 4, which is characterized in that: adjusting H in the step (2) according to the concentration of heavy metal in the waste liquid₂S partial pressure so that the regenerated eluent does not contain excessive H₂S。

6. The method for treating and recycling the heavy metal contaminated soil leaching waste liquid according to claim 1 or 2, which is characterized in that: heavy metal sulfide generated by the solid-liquid separation is recovered and used as a raw material of electroplating industry after being collected.

7. The method for leaching, regenerating and recycling heavy metal contaminated soil according to claim 1 or 2, wherein: the heavy metals in the soil also include one or more of cadmium, mercury, nickel or arsenic.

Background

With the rapid development of industrialization, people have an increasing demand for various metals. Heavy metals are mainly derived from activities such as industrial production, mining activities, waste treatment and the like, and the problem of heavy metal pollution of soil caused by excessive development and utilization of heavy metal resources by human beings has spread all over the world. Heavy metals have a great influence on the physicochemical properties of soil, such as pH, conductivity, cation exchange capacity, soil mineralogy and the like. Heavy metals cannot be decomposed by organisms in soil, but can be adsorbed by soil colloids and enriched by microorganisms and plants, and part of heavy metals enter the soil and can even be converted into substances with stronger toxicity, so that the human health is greatly threatened, and the problem of repairing the heavy metal contaminated soil needs to be solved urgently.

In recent years, soil remediation technologies such as solidification/stabilization remediation technology, electric remediation technology, leaching remediation technology, biological remediation technology and the like are rapidly developed, and leaching remediation methods have the advantages of short remediation period, good remediation effect, capability of extracting heavy metals from soil, avoidance of secondary pollution of subsequent heavy metals, low cost and the like, so that the leaching remediation method is widely concerned.

However, the soil leaching remediation process is often accompanied by the generation of a large amount of leaching waste liquid due to the non-degradability of the heavy metals and the requirement of a large solid-to-liquid ratio for obtaining a better leaching effect in the leaching remediation process. The leaching waste liquid needs to be treated, and secondary pollution can be caused by direct discharge; in addition, the regeneration and the recycling of the leaching solution are also considered, so that the treatment amount of the leaching waste solution can be reduced, the occupied area of equipment is saved, and the cost of the whole leaching process can be reduced. Therefore, the treatment and regeneration of the rinse waste liquid is generally considered as an integrated technical problem. The most important pollutant in the leaching waste liquid is heavy metal ions, and in order to enable the regenerated waste liquid to have a space for containing the heavy metal ions for recycling, the key point of the treatment lies in the separation process of the heavy metal ions. Heavy metals causing soil pollution have high contents of Pb, Cu, Zn and the like, have market value and are recycled. At present, the methods for solving the technical problems and realizing the regeneration of waste liquid and the recovery of heavy metals are mostly heavy metal ion precipitation separation methods, and part of the techniques are as follows:

patent CN111484161A discloses a method for treating heavy metal leaching waste liquid with organic sulfide, which separates heavy metal in the leaching waste liquid by flocculation precipitation, and removes excess organic sulfide by adsorption method to recycle the leaching waste liquid. CN108298666A discloses a method for treating heavy metal leaching waste liquid by sodium sulfide, heavy metal sulfide precipitate and EDTA sodium salt are generated by complexing heavy metal-EDTA with sodium sulfide, the recovered EDTA sodium salt can be recycled, however, the method does not mention how to treat excessive sodium sulfide in the solution, and the leaching agent is easy to directly precipitate heavy metal in the leaching process of the excessive sodium sulfide, so that the leaching efficiency of the heavy metal in soil is reduced. The patent CN1210503A and the patent CN109622583A adopt biological methods for precipitation, and both disclose a method for treating heavy metal leaching waste liquid by using sulfate reducing bacteria, wherein the sulfate reducing bacteria are directly used for treating SO₄ ^2-Transformation of S^2-Generating sulfide precipitate with heavy metal, and using sulfate reducing bacteria to remove SO from high-sulfur coal gangue₄ ^2-Transformation of S^2-Sulfide precipitates are generated with heavy metals, so that the leaching waste liquid can be recycled two to three times in an environment-friendly and efficient manner, but the content of substances in the soil leaching waste liquid is higherIn order to be complicated and the variation of pH is liable to cause inactivation of microorganisms, the practical application may require more complicated operation steps. In addition, the method disclosed in patent CN109604314A refers to a technique of precipitating heavy metals with hydrogen sulfide in a precipitation chamber, and the excess hydrogen sulfide is adsorbed by a pollutant adsorbent in an exhaust gas purification chamber; however, the method only treats the excessive hydrogen sulfide and does not solve the problem of excessive sulfur ions in the solution, and an additional adsorbent is also needed to treat the excessive hydrogen sulfide, so that the process cost is high.

The above-disclosed patents show that the method of generating sulfide precipitates is the most common technique for recycling the leaching waste liquid, since the solubility of heavy metal sulfides is very low and the complexation can be broken; the sulfide precipitation method has a certain application prospect, but no obvious effective and low-cost method exists on the problems of how to solve the problem of excessive sulfide in the regenerated waste liquid and avoid the influence on the heavy metal elution rate during the circulation of the waste liquid. In addition, the above techniques do not consider the problems of subsequent separation and utilization of heavy metal sulfide waste residues, and cannot reduce the waste liquid treatment cost from the perspective of final products. Therefore, the resource utilization of the generated heavy metal waste residues and the realization of the recycling of the leaching waste liquid at lower cost are the bottle necks which need to be broken through in the prior art, and a new method for leaching, treating, regenerating and recycling the heavy metal polluted soil is urgently needed to be designed.

Disclosure of Invention

Aiming at the defects and shortcomings of the prior art, the invention aims to provide a method for treating and regenerating and recycling heavy metal polluted soil leaching waste liquid, which utilizes a gas-liquid reaction to replace a common liquid-phase reaction and adjusts introduced H₂The volume of S gas realizes the step vulcanization of heavy metal in the leaching waste liquid, the formed heavy metal sulfide precipitate is selectively separated and recovered, and then the introduced H is strictly controlled₂The volume of S gas controls the amount of residual sulfide ions in the waste liquid, so that the treated eluent can be efficiently recycled.

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

a method for treating and recycling heavy metal contaminated soil leaching waste liquid is characterized by comprising the following steps:

(1) treating Pb, Cu and Zn heavy metal composite polluted soil by using a soil eluting agent, carrying out solid-liquid separation, and collecting soil eluting waste liquid containing Pb, Cu and Zn ions;

(2) introducing H into the leaching waste liquid₂S gas makes heavy metal step sulfurize, the step sulfurizing of the heavy metal is through adjusting H₂S is introduced into the waste liquid system by controlling H₂Partial pressure of S to control H₂S, the volume of the solution is increased, the step vulcanization of heavy metal is realized according to the difference of heavy metal Ksp, so that the solution sequentially generates CuS, PbS and ZnS, and the heavy metal sulfide precipitate is generated by step-by-step solid-liquid separation and recovery, so that the leaching waste liquid is regenerated into the soil leaching agent;

(3) and (4) treating the heavy metal contaminated soil by recycling the regenerated soil eluting agent.

Further, the eluent is inorganic strong acid solution such as dilute nitric acid and dilute sulfuric acid, or organic acid solution such as EDTA and citric acid, and the concentration is 0.25-1 mol/L.

Further, said H₂The volume of the S introduced into the waste liquid system is 3-25 mmol/L.

Further, the adjustment H₂The partial pressure method for introducing S into the waste liquid system comprises the following specific steps: introducing H into the leaching waste liquid₂3-4mmol/L of S gas, reacting for 5-15min, and performing solid-liquid separation; then introducing H into the rest liquid₂1-2mmol/L of S gas reacts for 5-15min, and then solid-liquid separation is carried out; then introducing H into the rest liquid₂12-20mmol/L of S gas, reacting for 5-15min, and performing solid-liquid separation.

Furthermore, the heavy metal sulfide precipitate generated by the solid-liquid separation is recovered and used as a raw material of electroplating industry.

Further, the heavy metals in the soil may also include one or more of cadmium, mercury, nickel, or arsenic.

Further, adjusting H in the step (2) according to the concentration of heavy metal in the waste liquid₂S partial pressure of gas, H introduced into the waste liquid system₂S bodyThe deposition just leads certain heavy metal to generate sulfide precipitation, and the regenerated leacheate does not contain redundant H₂S, the concentration of sulfur ions in the solution is kept at a very low level, and the reduction of the removal rate of heavy metals in the soil during recycling is avoided.

The principle of the invention is as follows: by means of H₂The S gas and the heavy metal ions are efficiently reacted to generate heavy metal sulfide precipitate, and different heavy metal sulfides K are utilized_spDifferent characteristics by adjusting H₂H with partial pressure of S gas adjusted to be appropriate₂S volume entering the reaction system, H₂S is decomposed in the system to produce S^2-Quantitative introduction of H₂S can be S in the system^2-Maintain a low concentration, K_spSmall heavy metal sulfides first form precipitates which are passed through K_spDifferent characteristics can realize the selective separation of heavy metals in the waste liquid and the introduction of H₂Compared with the S precipitation method, the traditional method of directly adding sulfide can cause S in the local part of the solution^2-Higher, not making S^2-The low concentration is kept, and the aim of selectively separating the heavy metals is not achieved. At the same time, nitric acid (HNO)₃) After the eluting agent is leached, a large amount of heavy metal ions can replace a large amount of H⁺More heavy metal nitrate exists in the leaching waste liquid, and the leaching waste liquid passes through H₂Heavy metal sulfide precipitate is generated after S treatment, and new H is introduced⁺So as to achieve the purpose of activating and regenerating the eluting agent, and the regenerated eluting agent can be recycled. Because H is quantitatively introduced based on the concentration of heavy metal ions in the waste liquid₂S, so that residual S in the regenerated eluent^2-The content is very low, and the reduction of the removal rate of heavy metals in the soil caused by the direct generation of metal sulfide precipitates is basically avoided in the process of recycling the soil.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) compared with the traditional precipitation method of metal sulfides such as sodium sulfide and the like, H₂S precipitation by adjusting H₂Partial pressure of S, control of H₂S enters the volume of the solution, the heavy metal stepped vulcanization is realized according to the difference of the heavy metal Ksp, so that the solution sequentially generates CuS, PbS and ZnS,so that various heavy metals can be separated and recovered step by step, the metal sulfide precipitates are not mixed together as usual, and the separation cost of heavy metals in the precipitates for subsequent recycling is reduced;

(2) selection of H₂S is used as a gaseous heavy metal precipitator and can ensure S in a solution system^2-Evenly distributed, avoiding S in a solution system caused by directly adding solid sulfide^2-In the case of local concentration being too high, H is caused₂The reaction rate of S is greatly improved, and H is accurately controlled₂The introduction amount of S can just ensure that certain heavy metal generates sulfide precipitation, and finally, redundant H cannot be generated₂S enters the solution, so that the concentration of sulfur ions in the solution is kept at a very low level, and compared with the traditional sodium sulfide precipitation method, the method reduces the subsequent process of sulfur ion precipitation treatment, saves sulfide raw materials and avoids the generation of sulfur simple substance waste residues in the sulfur ion treatment process;

(3) based on the content of heavy metal ions in the waste liquid, H is accurately controlled₂The introduction amount of S is such that the residual S in the regenerated eluent^2-The content is very low, and the condition of directly generating metal sulfide precipitate basically does not occur in the process of recycling and treating the soil, so that heavy metals in the soil can still enter leacheate, and the metal removal rate of the soil is not greatly reduced;

(4) selection of H₂S used as heavy metal precipitator can not only precipitate heavy metal sulfide, but also supplement a large amount of H⁺And the eluent enters a solution system, and impurity metal ions such as Na and the like are not introduced, so that the eluent is activated and regenerated again and can be recycled.

Drawings

FIG. 1 shows the difference H in example 1₂S, a graph of the removal efficiency of the heavy metal under the input quantity;

FIG. 2 is H in example 2₂A graph showing the change of the removal rate of the heavy metal with time at an S introduction amount of 3.33 mmol/L;

FIG. 3 shows H in example 2₂S is a graph showing the change of the removal rate of heavy metals with time at an introduction amount of 5 mmol/L;

FIG. 4 shows H in example 2₂S is introduced into the reactor at a rate of 20mmol/L of lower heavy metalA plot of removal rate versus time;

FIG. 5 shows the removal rate of heavy metals with time H in example 3₂S, a change chart of the input amount;

FIG. 6 is a graph showing the removal rate of heavy metals from soil after each cycle of elution reagent regeneration in example 4.

Detailed Description

The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.

To is directed atSoil of certain heavy metal polluted siteThe experiment shows that the main heavy metal pollutants are Pb, Cu and Zn, the total Pb and Cu content is about 2000mg/kg, and the total Zn content is about 20000 mg/kg. Leaching the polluted soil by adopting a leaching agent (the leaching agent is 0.5mol/L dilute nitric acid) with the solid-to-liquid ratio of 1:5, reacting for 30min, and collecting leaching waste liquid after leaching.

Example 1

Preparing a soil eluting agent, treating Pb, Cu and Zn compound contaminated soil for 30min by the eluting agent according to a solid-liquid ratio of 1:5, and collecting the Pb, Cu and Zn-containing soil eluting waste liquid. And preparing hydrogen sulfide, collecting saturated hydrogen sulfide solution by using a gas storage tank, and sealing paraffin for later use. Measuring 1L of leaching waste liquid, and controlling H through a flowmeter₂S gas flow, respectively introducing H into the leaching waste liquid₂S gas is 0.5, 1, 5, 10, 20, 30 and 50mmol/L, solid-liquid separation is carried out after 5min of reaction, and ICP is used for detecting the heavy metal removal effect of the waste liquid.

The results in FIG. 1 show that when H is₂When the concentration of S gas reaches 5mmol/L, the maximum removal rate of Cu and Pb is close to 100 percent, and when H is in use₂When the concentration of S gas reaches 20mmol/L, the maximum removal rate of Zn approaches 100%. By adjusting the introduction of H₂The concentration of S gas can selectively separate and recover heavy metal sulfide precipitate.

Example 2

Preparing a soil eluting agent, treating Pb, Cu and Zn compound contaminated soil for 30min by the eluting agent according to a solid-liquid ratio of 1:5, and collecting the Pb, Cu and Zn-containing soil eluting waste liquid. And preparing hydrogen sulfide, collecting saturated hydrogen sulfide solution by using a gas storage tank, and sealing paraffin for later use. Measuring leaching waste liquid 1L, controlling H by a flowmeter₂S gas flow, respectively introducing H into the leaching waste liquid₂3.33, 5 and 20mmol/L S gas, 3 groups of experiments, solid-liquid separation after reaction for 1, 2, 5, 10, 20 and 30min, and ICP (inductively coupled plasma) detection of the effect of removing heavy metal in waste liquid and the effect of separating heavy metal by step precipitation.

The results of FIGS. 2-4 show that H₂S sequentially carrying out precipitation on Cu, Pb and Zn, wherein only Cu is precipitated under the low concentration of 3.33mmol/L, and the precipitation rate is close to 100% in about 5 min; under the concentration of 5mmol/L, Cu and Pb are nearly completely precipitated within about 5min, and Zn is still not precipitated; at a concentration of 20mmol, Zn is nearly completely precipitated in about 5 min.

Example 3

Preparing a soil eluting agent, treating Pb, Cu and Zn compound contaminated soil for 30min by the eluting agent according to a solid-liquid ratio of 1:5, and collecting the Pb, Cu and Zn-containing soil eluting waste liquid. And preparing hydrogen sulfide, collecting saturated hydrogen sulfide solution by using a gas storage tank, and sealing paraffin for later use. Measuring 1L of leaching waste liquid, and controlling H through a flowmeter₂S gas flow, introducing H with the volume of 3.33mmol/L into the leaching waste liquid₂S gas reacts for 10min, solid-liquid separation is carried out, a small amount of liquid is taken for testing, and H with the volume of 1.67mmol/L is introduced into the residual liquid₂S gas reacts for 10min, solid-liquid separation is carried out, a small amount of liquid is taken for testing, and H with the volume of 15mmol/L is introduced into the residual liquid₂And S, reacting for 10min, performing solid-liquid separation, taking the residual liquid to be detected, and detecting the heavy metal removal effect of the waste liquid and the effect of gradient precipitation separation of the heavy metal by using ICP (inductively coupled plasma).

The results of FIG. 5 show that by controlling H₂The S gas can be introduced to precipitate Cu, Pb and Zn in sequence, and the aim of separating heavy metals Cu, Pb and Zn by step precipitation can be fulfilled.

Example 4

Preparing a soil eluting agent, treating Pb, Cu and Zn compound contaminated soil for 30min by the eluting agent according to a solid-liquid ratio of 1:5, and collecting the Pb, Cu and Zn-containing soil eluting waste liquid. Measuring 1L of leaching waste liquid, and controlling H through a flowmeter₂S gas flow, introducing H into the leaching waste liquid₂Reacting S gas 20mmol/L for 5min, separating solid and liquid, and usingAnd (3) leaching the soil by using the supernatant, performing acid digestion on the leached soil, detecting the concentration of heavy metal in the soil digestion solution by using ICP (inductively coupled plasma), and calculating the effect of the leaching treatment on the removal of the heavy metal in the soil.

The results in FIG. 6 show that the removal rate of heavy metals from soil after each leaching can be maintained at a substantially consistent level, H₂The leaching waste liquid after the S gas process treatment has the capacity of recycling.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.