KR101610259B1 - Method for evaluating and determining acid producing potential of rocks - Google Patents

Abstract

The present invention relates to a method for evaluating the amount of acid production of mine waste.
The method for evaluating and determining the amount of acid production of mine waste according to the present invention is characterized in that the acid generation of the sample, the acid rain generation group, and the uncertainty of the acid generation are determined through the ABA (Acid Base Accounting) test and the NAG (Net Acid Generation) In the preliminary evaluation stage and the preliminary evaluation stage, which are classified as a group, the precision evaluation stage is carried out for the samples which are found to be uncertain.
The precision evaluation stage is a first test step of measuring the total amount of sulfide minerals composed of chemical species capable of generating acidic drainage through the analysis of the chemical species of the sulfide minerals contained in the sample and converting them into the acidity of the sample, A second test step for measuring the neutralization ability of the sample by applying the test method, a NAG test method for the sample, and a turbid solution after the NAG test method to exclude the influence of the organic acid generated in the NAG test method A third test step of oxidizing and decomposing the organic acid again and measuring the amount of acid generated in the sample, and an evaluation step of evaluating the probability of occurrence of acidity of the sample using the results of the first test step to the third test step Feature.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a technology related to restoration of environment. More specifically, the present invention relates to a technology for restoring the environment, and more particularly, to a method of detecting acid rain drainage by contacting a pile of rock or waste stone exposed to mine waste, To determine the amount of acid generated.

 Human development activities, such as mine development and civil engineering, are disturbed by chemically stable rocks in the ground and exposed to the atmosphere and water. At this time, minerals containing sulfur in rocks can generate acidic drainage through the oxidation process. Acid drainage generally exhibits low pH and high concentrations of heavy metals and sulphates and adversely affects the ecosystem, as well as iron oxide precipitated in the water (enrichment phenomenon, see photo in Fig. 1) and aluminum oxide ) Seriously undermines the natural landscape.

In order to minimize the damage from these acid wastewater, it is necessary to pre-evaluate and determine whether a specific area generates acidic wastewater.

Methods for evaluating the acid production of rock samples have been continuously studied by various researchers since the 1970s. Although these evaluation techniques show some differences in the chemicals used in the experiment, the reaction temperature, and the reaction time, the maximum acidity and acid neutralization capacity of the rock samples are compulsorily implemented through physicochemical test methods, = Acidogenic activity - acid neutralizing activity).

In order to evaluate the acid production of rock samples up to now, the evaluation techniques mainly used in Korea and abroad are ABA (Sobek et al., 1978) and NAC (Miler et al., 1997) And concurrently considers the results. The ABA test consisted of Total S analysis and Acid Neutralizing Capacity (ANC) tests, which were conducted to derive the maximum potential ability (MPA) and acid neutralization capacity, Can be predicted.

The amount of acid production obtained through the ABA test is called NAPP (Net Acid Producing Potential = Tota S - ANC). When it is larger than 0, acid is generated. In the NAG test, the amount of acid production, which takes into account both acidity and acid neutralization ability, can be directly obtained from the experimental characteristics. In addition, the final pH (NAGpH) value of the NAG test does not directly indicate the amount of acid production, but is an indicator for indirectly determining whether or not the acid is generated. It is classified as a sample that generates acid when NAGpH is smaller than pH 4.5 and does not generate acid when it is larger than 4.5. Consideration of NAPPH obtained from the ABA test and NAGpH obtained from the NAG test can be used to evaluate the acid generation of the sample.

The graph of FIG. 3 is an example of evaluating the amount of acid production of a rock sample through the existing acid generation evaluation technique. The fourth quadrant of the graph shown in FIG. 3 is an area in which acidity occurs in both the ABA test and the NAG test, and is classified into a potential acid forming (PAF) group. The second quadrant means that no acid occurs in both tests and is classified as NAF (Non-Acid Forming). However, the samples in the first and third quadrants are classified as uncertain (UC) when the two test results are different from each other. The reason why the sample is judged to be uncertain is due to the assumptions on which the ABA and NAG tests are based.

First, in the case of the Total S experiment of the ABA test, it is assumed that all the sulfur present in the sample is present in the form of pyrite, which is a representative mineral that generates acid, and the total sulfur content in the sample is measured and theoretically occurs through the stoichiometric method Calculate the maximum possible scattering power. In general, however, in the natural state, in addition to the sulfide minerals represented by pyrite, sulfur may exist as sulfates, organic sulfur, and elemental sulfur. A large error may occur. In the ANC test, acid neutralization capacity is determined by dissolving neutralized minerals using hydrochloric acid of a predetermined volume and concentration and calculating the acid neutralization ability by dissolved neutralized minus through back titration. At this time, the determined ANC is a neutralization function of the total amount concept, but there is a concern that some neutralized minerals may not be expressed in the natural pH range or may be overestimated if they are considered in the ANC. There is also a cause for the NAG test to determine the sample as uncertain. The NAG test calculates acid production by inverse titration of the total amount of acid generated by forced oxidation of sulfide minerals present in the sample through hydrogen peroxide. In this case, organic carbon and organic sulfur which do not generate acid in the natural state can generate acid under strong oxidizing condition using hydrogen peroxide, so that the acid generation amount of the sample can be overestimated.

Existing acid abatement assessment techniques are often classified as uncertain due to limitations inherent in the method itself. In this case, in order to evaluate the acidity of the sample properly, it is necessary to perform additional kinetic tests to directly simulate the weathering of the sample, You must do what you need to do. In this case, it takes a long time and effort to evaluate the acidity of the sample (short time is several days to several years), and it is very dependent on the subjective judgment of the researcher.

The problems of the existing evaluation method are summarized in Table 1 below.

[Table 1]

Therefore, it is required to develop a precise evaluation technique which can judge whether or not acid is generated by the sample which has not been evaluated by the existing acid emission evaluation technique.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an acid generation evaluation and determination method capable of economically and highly accurately evaluating whether or not rocks such as mine waste, The purpose is to provide.

In order to achieve the above object, the present invention provides a method for evaluating and determining the amount of acid waste generated in a mine waste, comprising the steps of: analyzing chemical species of the sulfide minerals contained in the sample to generate acidic drainage; A first test step of measuring the total amount of the sulfide minerals comprising the chemical species and converting the total amount of the sulfide minerals into the acidity of the sample; A second test step of measuring the neutralization ability of the sample by applying the ABCC test method to the sample; After the NAG test method is performed on the sample, the turbidity of the turbid solution after the NAG test method is again oxidized to exclude the influence of the organic acid generated in the NAG test method, thereby oxidizing and decomposing the organic acid. A third test step of measuring the amount of generation; And evaluating an acid generation probability of the sample using the results of the first to third test steps.

According to the present invention, after the sulfide minerals are classified into acid-generating sulfides, acid-generating sulfates, non-acid generating sulfates and other sulfides in the above-mentioned samples, in the first test step, the total amount of acid-generating sulfides and acid- Is calculated and converted into an acidogenic ability.

The KCl extraction method is used to measure the total amount of the acid-generating sulfate, and the CRS test can be used to measure the total amount of the acid-generating sulfide.

In one embodiment of the present invention, the titration is performed until the target pH is reached while repeatedly adding hydrochloric acid to the sample in the second test step, and stirring is performed at a reaction time of 1,000 seconds or more when hydrochloric acid is once added desirable.

In one embodiment of the present invention, in the third test step, the measurement of the acid generation amount of the sample is performed by an Extended NAG method of measuring the turbidity of the oxidized and decomposed organic acid by titration or a Calculated NAG Method can be used.

In order to oxidatively decompose the organic acid in the third test step, hydrogen peroxide is preferably added to the sample and heated to a boiling point or higher.

In one embodiment of the present invention, in the evaluation step, the difference value of the acid neutralizing ability between the acid value of the sample, which is the result of the first test step, and the result of the second test step, The first acid generation amount and the result of the third test step are set as the X axis and the Y axis, respectively, and then the sample corresponding to the first quadrant formed by the X axis and the Y axis is set as the acid Samples corresponding to the quadrants and quadrants are to be evaluated as uncertainty samples, and those corresponding to quadrant 3 are to be evaluated and determined as samples to be generated.

Meanwhile, in the present invention, a pre-evaluation step and a precision evaluation step can be performed to evaluate whether or not an acid of a rock sample is generated. That is, the present invention is a preliminary evaluation step of classifying an acid generation occurrence of the sample into an acid generation group, an acid rain generation group, and an uncertainty group through ABA (Acid Base Accounting) test and NAG (Net Acid Generation) And a precise evaluation step for a sample identified as an uncertainty group in the preliminary evaluation step to evaluate whether or not an acid of the sample is generated. The precision evaluation step uses the above-described estimation and determination method of the amount of generated municipal waste acid .

The method for estimating the amount of acid production of mine waste according to the present invention has the advantage that it is possible to more clearly evaluate and determine whether the acid is generated by improving all points indicated as inherent limitations of the existing evaluation method.

In addition, the present invention improves the economical efficiency and applicability of the experimental procedure by performing the preliminary evaluation according to the existing method and performing the precise evaluation only for the sample in which the occurrence of the acid is uncertain in the preliminary evaluation.

The precision evaluation method proposed by the present invention can be widely used for the civil engineering work or the management of the abandoned mine area.

FIG. 1 and FIG. 2 are photographs of examples of damages of the surrounding environment by acidic mine drainage. FIG. 1 is an example of redevelopment by iron oxide, and FIG. 2 is an example of redevelopment by aluminum oxide.
The graph of FIG. 3 is an example of evaluating the amount of acid production of a rock sample through the existing acid generation evaluation technique.
In FIG. 4, the method according to the second embodiment of the present invention is summarized in a schematic flow chart, and in FIG. 4, only the method of the first embodiment of the present invention is shown.
5 is a schematic diagram for explaining the CRS test.
6 is a graph showing the ABCC test results.
FIG. 7 is a graph showing the results of comparison of the amount of acid production obtained by using the existing method (Total S) (calculated as the total sulfur content) and the improvement method employed in the present invention (calculation considering the sulfur species).
FIG. 8 is a graph comparing the results of applying the conventional method (ANC) and the improvement method (ABCC) to the sample in order to evaluate the neutralizing ability of the sample.
FIG. 9 shows Fourier transform infrared spectroscopy (FT-IR) analysis of three samples C2, C4, and D3 under three conditions (33 = 9) after the reaction, before the ABCC reaction, and after the ANC reaction The results are shown.
10 is a graph of XRD data and quantitative analysis results of C2, C4, and D3 samples.
FIG. 11 shows a graph of a comparison between the conventional NAG pH and the Extended NAG pH employed in the present invention.
12 is a graph comparing an existing NAG with an extended NAG and a calculated NAG employed in the present invention.
FIG. 13 (existing method) and FIG. 14 (present invention) are graphs showing the relationship (correlation R ² by the least squares method) between the existing method and the acid generation evaluation index obtained by the method according to the present invention.

The method of evaluating and determining the amount of generated acid according to the present invention is characterized by introducing experimental methods to complement and improve the above-mentioned existing limit of the amount of acid generation evaluation technique. It is also advantageous that the experimental procedure is simplified for the convenience of users within the range that does not affect the experimental results.

In the present invention, two types of methods are proposed. The first type of method is made up only of the core techniques of the present invention. The second type of method is to expand the economical efficiency and applicability of the estimation of acid production amount by combining core techniques (precision evaluation method) and preliminary evaluation methods.

In FIG. 4, the method of the second form of the present invention is summarized in a schematic flow chart. In FIG. 4, the two-step method shows only the method of the first form of the present invention. For convenience of explanation, the term including the entirety of Fig. 4 is referred to as "overall evaluation method ", and only the second step is detached in Fig. The present invention includes both an overall evaluation method and a precision evaluation method.

Table 2 below summarizes the improvements in the precision evaluation method according to the present invention. [Table 2] shows that the existing Total S test was improved by Sulfur speciation, and the ANC test was improved by ABCC (Acid Buffering Characteristic Curve) test. The existing NAG test was replaced by the modified NAG test and the extended NAG test or the calculated NAG test was performed in detail.

Sulfur species analysis (first test step) consists of KCl extraction to classify acidogenic sulphate minerals and Chromium Reducible Sulfur (CRS) tests to classify acidogenic sulphide minerals . Therefore, it is possible to overcome the limitation of the total S experiment that assumes all the sulfur in the sample as the sulfide mineral through the analysis of sulfur species species. Specific test methods will be described in detail later.

The ABCC test (second test step) is similar to ANC in that it reacts with neutralizing substances in the sample using hydrochloric acid, but differs in that the sample reacts more slowly and gradually with hydrochloric acid. ABCC reacts with the sample using hydrochloric acid, but unlike ANC, which injects the determined acid at one time, it injects a small amount of acid several times. In addition, at each step of introducing the acid, reaction time of more than 1,000 seconds is provided to create an environment in which the input acid can completely react with the neutralizing material. These experimental differences allow ABCC to identify pH changes with acid input. Since ANC calculates the total neutralizing capacity of a sample by using strong acid, it can consider acid neutralizing ability which is not generated in a natural state. However, when ABCC is used, acid neutralizing ability which can be readily available in acid can be distinguished. Can be analyzed to evaluate the substances exhibiting acid neutralization ability. Specific test methods will be described in detail later.

In the conventional NAG process, when carbonaceous materials are forcibly oxidized by hydrogen peroxide, organic acids are generated, which may affect the amount of acid generated and the NAGpH value. However, these organic acids are acids that are not related to the acids generated by the sulfide minerals and do not occur in the natural state, so they should be excluded from the NAG calculation. Therefore, the Modified NAG test (the third test step) used in the present invention is designed to exclude these organic acids from the acid generation evaluation through two methods (Extended NAG, Calculated NAG). Extended NAG is a method of decomposing organic acids by further adding strong oxidizing conditions. Calculated NAG is a method of eliminating organic acids in calculation of acidity and acid neutralization ability through ion analysis. Specific test methods will be described in detail later.

As described above, the precision evaluation method according to the present invention is composed of sulfur chemical species analysis, ABCC, and modified NAG, and it is evaluated (evaluation step) whether the acid is generated by the similar principle, experimental method, . In other words, acidification ability is calculated by analyzing the sulfur species replacing Total S, and acid neutralization ability is obtained by ABCC which can replace ANC, and the acid production amount (NAPP) is calculated by the difference of the two values. In addition, the amount of acid production (NAG) can be calculated through Modified NAG which improved the NAG experiment. In the NAPP vs NAG graph, similar to the existing acid yield estimation technique, the first quadrant means that the acid is generated in both experiments, and the samples shown in this area are classified as acid generation samples (PAF). Likewise, quadrant 3 is categorized as acid-free (NAF), and samples 2 and 4 refer to uncertain (UC) samples. As in the case of the conventional acid discharge estimation method, the uncertainty group can be evaluated in the accurate estimation method of acid generation, but it can occur in the theoretically very rare case. In this study, too, the experiment was performed on various samples. Not found.

Hereinafter, each test of the overall evaluation method according to the present invention will be described in turn. The overall evaluation method consists of a preprocessing step, a first step (preliminary evaluation step), and a second step (precision evaluation step).

1. Pre-processing step

In the pretreatment step, samples are taken first. When collecting samples, you should choose samples that can represent the area you want to evaluate. This is because, even in the same region and geology, the amount of acid production depending on the exposure and weathering degree of the sample may show a large difference. The specimens collected from the field are pre-treated for laboratory tests through processes such as grinding (<75 μm), grinding and air-drying.

2. Pre-evaluation stage (stage 1)

In the preliminary evaluation stage, ABA test and NAG test, which are widely used, are performed. The ABA test again consists of the Total S test and the ANC test.

- Total S test

The total S test is the process of calculating the maximum potential acidity after assuming the total sulfur content in the sample and assuming it to be all pyrite. There are various methods for obtaining total sulfur content, but C, S analyzer, elemental analyzer, XRF and the like are widely used. The total sulfur content (%) is multiplied by a conversion factor of 30.6 and converted into the acidity (kg H ₂ SO ₄ / t). However, if converted to% CaCO ₃ , multiply by the conversion factor 3.13. The units expressing the acidogenic ability are divided into two groups of kg H ₂ SO ₄ / t and% CaCO _3. The former is a unit in the concept of total amount of acid generated and the latter means the amount of neutralizing agent neutralizing it. The unit to be used shall be determined according to the purpose of the test, and the same acid neutralizing ability and acid production amount to be determined in the remaining test shall be used.

- ANC examination

In the ANC test, 1 ~ 2 drops of 8% hydrochloric acid are reacted with the sample to determine the amount of hydrochloric acid and titrant to be added (Fizz evaluation) by referring to [Table 2] according to the degree of bubbles generated. If the ANC of the sample can be predicted, this step can be omitted.

[Table 2]

Add 2 g of the pretreated sample and hydrochloric acid determined in step 1 into a 250 ml flask, and use 20 ml of distilled water to react both the sample on the wall and the hydrochloric acid. In this case, the blank without sample is experimented with the same procedure, but it is a very important parameter. Therefore, it is recommended to use two or more control experiments for each bubble generation class and use the average value.

The flask containing the suspension is then heated to 80-90 ° C. on a heating plate and heated until the reaction is complete (minimum 2 h). In this case, in order to prevent the rapid evaporation of the turbid solution, cover the glass plate and keep the experimental conditions uniform by shaking the turbid solution or adding distilled water to the mixture.

Then, add distilled water to the reaction solution, adjust volume to 125 ml, and warm to room temperature. The pH of the turbid solution is measured and the appropriateness of the experiment is evaluated based on the following [Table 3].

[Table 3]

Then, the turbid solution is titrated to pH 7 using the sodium hydroxide determined in step 1. At this time, when pH 5 is reached, 1 ~ 2 drops of 30% hydrogen peroxide is added to perform the process of oxidizing iron ions.

Finally, the ANC value is obtained by the following equation.

The ANC test is an experiment to determine the acid neutralization ability, and it starts with the assumption that the representative neutralizing substances capable of neutralizing the acid are calcium carbonate and magnesium carbonate. This test method reacts acid with the sample, knowing the concentration and volume, taking into account that the carbonate reacts actively with the acid. The Fizz evaluation is to determine the amount of acid input by roughly grasping the carbonate content through the amount of CO ₂ generated by the reaction of acid and carbonate.

CaCO ₃ + 2HCl = CaCl ₂ + CO ₂ + H ₂ O

An example of determining the concentration and volume of hydrochloric acid according to the degree of bubble formation in the Fizz evaluation is shown in the above experimental procedure. However, since the Fizz evaluation is a very subjective experiment, the concentration of hydrochloric acid is not meaningful and it is a recommended value for the convenience of the experiment, and it can be reasonably modified according to the convenience of the user. After the hydrochloric acid determined by the Fizz evaluation has reacted with the sample, the pH of the solution can be measured to evaluate the appropriate amount of hydrochloric acid. In order to evaluate acid neutralization ability more accurately, it is necessary to repeatedly perform ANC to determine a suitable amount of hydrochloric acid.

When reacted hydrochloric acid is reacted with the sample, the temperature of the turbid solution is set to about 80 to 90 ° C to improve the reaction speed (until the reaction is terminated) It should be heated for at least 2 hours and the solution should be shaken occasionally and filled with evaporated water to maintain a constant volume. This process assumes that all carbonate minerals consume acid and dissolve.

After the reaction has been completed, the temperature of the turbid solution is lowered to room temperature, and the pH is measured to confirm the suitability of the hydrochloric acid input. The amount of acid remaining unreacted with the sample is derived by back titration to pH 7 using sodium hydroxide determined in the Fizz evaluation. The titration agent used at this time can be reasonably adjusted by the user considering the easiness of the experiment. When the amount of acid added and the difference of acid not consumed are obtained, the amount of acid consumed in reaction with the sample can be calculated and the acid neutralizing ability can be obtained by unit conversion. However, in the titration process, 2 drops of 30% hydrogen peroxide are added to the turbid solution having reached pH 5, and the reaction is continued for about 5 minutes to maintain the oxidation reaction of the turbid solution. Through this process, the oxidation of Fe ²⁺ present in the turbid solution is promoted, which minimizes the overestimation of the acid neutralizing ability.

- NAG test

In the NAG test, 2.5 g of pretreated sample is first crushed to a size of 200 or less, air dried, and placed in a 500 ml beaker. Add 250 ml of 15% hydrogen peroxide to the above reaction vessel and start the experiment. Cover the top of the vessel with a glass dish. At this time, in the case of the sample having a high sulfur content, boiling occurs due to reaction with hydrogen peroxide, so that the high-temperature turbid liquid may overflow or splash out of the vessel. For these samples, the weight of the sample may be reduced or the reaction may be delayed using distilled water. Since hydrogen peroxide may oxidize with the sample, it may cause harmful gas. Therefore, it should be experimented in the hood and stir the turbid liquid temporarily or add distilled water until the reaction is completed to fill the evaporated turbid liquid. The experiment is considered to be terminated when the bubble formation of the turbid fluid is stopped and the sample is clarified and settled in the turbid liquid. Depending on the sample, the reaction time varies from hours to tens of hours. After completion of the reaction, the suspension is heated at 80 to 90 ° C for at least 2 hours using a heating plate to decompose surplus hydrogen peroxide. At this time, distilled water is appropriately added to maintain the volume of the sample. After the reaction has been completed, the suspension is warmed to room temperature, rinsed with distilled water, and the volume is adjusted to 250 ml. When the pH of this solution is measured, it becomes NAGpH. If NAGpH is 2 or more, 0.1 M sodium hydroxide is used. If it is less than 2, the pH of the suspension is titrated to 4.5 with 0.5 M sodium hydroxide.

The NAG experiment is an experiment in which hydrogen peroxide, a powerful oxidizing agent, is reacted with a sample to simulate the weathering of the sample in a short time. The added hydrogen peroxide reacts with the available sulfide minerals in the sample and develops acidogenic ability. The generated acid reacts with minerals that exhibit acid neutralizing activity in the sample at the same time. Therefore, unlike the ABA experiment, which is a separate experiment, NAG experiment is an experiment that can measure the amount of final acid that takes into account the acidity and acid neutralization ability in a single experiment. In addition, NAG experiments theoretically take into account the amount of acid that can be expressed within the reaction with hydrogen peroxide, unlike ABA, which derives maximum acidogenic capacity and maximum acid neutralization capacity. Since the NAG experiment is a process for oxidizing potentially sporadic minerals by using hydrogen peroxide, the amount of acid that is calculated by the NAG experiment is sufficient when the acid neutralization ability of the sample is insufficient, And the total amount of acid neutralizing ability can not be obtained directly. However, it can be indirectly evaluated by measuring the pH (NAGpH) of the reaction solution. NAGpH is considered to be a sample that generates acid if it is less than 4.5 and a sample that does not generate acid if it is more than 4.5.

As described above, in the preliminary evaluation stage, whether the acid is generated by the ABA test or the NAG test, which is widely used, is judged and classified into the acid generation group, the acid rain generation group and the uncertainty group. For the samples identified as uncertain in the preliminary evaluation stage, the second stage (precision evaluation stage) is performed subsequently. Although it is possible to judge whether or not the acid is generated by performing the precision evaluation step from the beginning with respect to all the samples, it is preferable to perform the precision evaluation only for the uncertainty group because the precision evaluation is more complicated and takes more time than the preceding evaluation step. In addition, in the preliminary evaluation stage, the samples classified into the acid generation group and the acid rain generation group are judged to be the same even if the precision evaluation is performed. Therefore, for the economical efficiency of the evaluation, To perform a precision evaluation.

3. Precision evaluation stage (stage 2)

The precision evaluation stage consists of a first test step (sulfur speciation) for obtaining the total amount of sulfate and sulfide capable of generating acid, particularly through the analysis of sulfur species in the sample, and a second test step (ABCC test ), A third test step (modified NAG) for measuring the amount of acid generated after eliminating the influence of the organic acid generated through the NAG test, and the values measured in the first to third test steps, And an evaluation step of judging whether or not there is an abnormality. Explain it in order.

- Sulfur speciation (first test step)

Sulfer speciation is again determined by the amount of sulfate (KCl extraction method) and sulfide (CRS test) that can generate acid in the sample through KCl extraction and CRS test.

* KCl extraction method

The KCl extraction method is based on the reaction of the sample and the KCl solution and measuring the acidity by titration through an experiment which is focused on the characteristic that the sulfate minerals are well dissolved in KCl. The KCl solution should be thoroughly flushed with argon, an inert gas before use, to remove oxygen as much as possible. This is because if the oxygen in the KCl solution reacts with the sample, some unexpected sulfide minerals may be oxidized. Sulfate minerals dissolving through the KCl solution are divided into acid-generated sulfate and acid-unexplained sulfate. The acid titre sulfate is measured by back titration, which is the method used to calculate ANC and NAG same. An example of the test is shown in 1 to 8 below.

[KCl extraction test example]

1. Prepare a 1 M KCl solution filled with argon gas for at least 30 minutes.

2. Quantify 2 g of sample sieved below 75 (200) and place in a 125-ml reaction vessel and add 80 ml of the prepared KCl solution to the reaction vessel containing the sample.

3. Fill the reaction vessel with argon gas to remove the oxygen in the empty space remaining at the top of the reaction vessel and seal the reaction vessel well.

4. Continue to stir the reaction vessel containing sample and KCl solution for 1 hour.

5. At the end of the reaction, filter out the reaction solution using 0.45 filter paper.

6. Extract a portion (about 30-50 ml) of the reaction solution and titrate it to pH 7.0 using titration agent (NaOH) to obtain the acidity. Only about 2 drops of hydrogen peroxide (20 uL) are added at around pH 5.0 to perform the dissolved iron oxidation process in solution. When the pH of the reaction solution is less than 4, titration can be performed using 0.01 M NaOH when 0.1 M NaOH is 4 or more.

7. Perform ion analysis by measuring the concentration of dissolved S, Fe, Ca, Mg, Al, and Na through the remaining solution. The total amount of acid-producing and non-acid-producing sulfate minerals can be calculated through this process. This step can be omitted if only acid-producing sulphate minerals are required, not total sulphate minerals.

8. The amount of sulfate to be finally obtained is determined by the following formula.

* CRS test method

The CRS test is based on the conversion of the reduced form of inorganic sulfur to H ₂ S form using a CrCl ₂ solution of high temperature and strong acid. Reduced forms of sulfur include iron disulfide, organic sulfur, and volatile sulphide minerals (greigite, mackinawite, etc.). Iron sulphide content is generally high, most of which is sulfide minerals such as pyrite. In this experiment, organic sulfur can be recovered together, but the amount of organic sulfur in the natural state is negligible. If the content of organic sulfur and volatile sulfuric acid is high in the sample, Can be designed.

In order to react the sample with CrCl ₂ , chromium and ethanol are placed on the heating plate shown in the schematic diagram of FIG. 5 together with the sample. When N ₂ gas is fed to transfer the H ₂ S gas generated from the sulfide minerals and the flow is stabilized, the hydrochloric acid stored in the funnel is supplied to start the reaction. As the reaction progresses, the sulfide minerals are reduced to H ₂ S and transferred to a flask containing zinc acetate according to the flow of nitrogen gas. When passing through the condenser, all of the water condenses and collects on a hot plate, and only the gas components (mainly H ₂ S) can be transferred to the flask. The H ₂ S gas reacts with the zinc acetate solution in the flask and is collected and converted into ZnS, and ZnS can be quantified by iodine titration after completion of the experiment. The following is an example of the CRS test from 1 to 9.

[CRS Test Example]

1. Prepare the samples pretreated by differential drying, air-dried, and quantitated according to the criteria given in Table 5 below and put them in a round flask. All procedures are applied to Blank.

[Table 5]

2. Add 2.0 g of chromium and 10 mL of 95% ethanol into a round flask and shake to wipe the sample. The round flask is then placed on a heating plate and a condenser, funnel, etc. are connected. The experiment must be performed in the hood.

3. Place 40 mL zinc acetate in a 100 mL Erlenmeyer flask and connect the glass tube to the correct height. Make sure that the water flows around the condenser and that the blast flow is well secured.

4. Add 60 mL of 6M HCl to the funnel. Connect nitrogen gas to the funnel and adjust the pressure to a level that will cause three bubbles per second in the zinc acetate solution. Allow to flow for 3 minutes to fill the entire system with nitrogen.

5. Slowly add the hydrochloric acid in the funnel to a round flask.

6. Wait for 2 minutes and heat to boiling. Keep the decomposition process for about 20 minutes and check that the H ₂ S gas generated during this process flows well through the condenser.

7. When the reaction is complete, remove the Erlenmeyer flask and rinse the remaining ZnS in the glass tube and Erlenmeyer flask with 20 mL of 6M HCl to recover all the ZnS in the Erlenmeyer flask.

8. Oxidation-reduction titration of zinc acetate solution through iodine solution.

9. Calculate the amount of sulfide using the formula below.

- ABCC test (second test step)

The ABCC test is similar to ANC in that it reacts with neutralizing substances in the sample using acid, but differs in that it reacts slowly and gradually. In ABCC, hydrochloric acid is used to react with the sample, but the reaction time is more than 1,000 seconds and acid is added little by little. Therefore, depending on the sample, the experiment may take several hours to several days. It is recommended to use the automatic titrator. Although the recommended amount of acid to be reacted with the sample is based on the ANC concentration, it can be reasonably modified according to the subject of the experiment. ABCC experiments can be used to distinguish readily available acid neutralizing ability among substances involved in acid neutralizing ability and to evaluate acid neutralizing ability through proper curve characteristics.

6 shows an example of ABCC test result. Since the time interval of injecting the acid is sufficiently long, the amount of acid introduced into the x-axis, that is, the amount of acid reacted with the sample, can be regarded as the pH change along the y-axis. In the following experimental example, it was confirmed that the acid neutralization ability of the sample A was shown by the addition of the acid, the pH was maintained in the range of 7 to 8, and then rapidly decreased after the acid of 55 kg of H ₂ SO ₄ / t was added. As the acid was added and the pH began to drop sharply, the pH remained constant from 4. This means that Sample A is higher in acid neutralizing ability that can be expressed immediately than Sample B, even though the initial pH is similar. In addition, sample C showed lower pH 5 than sample B at the beginning of the reaction, but behaves similar to that of sample B, and it is expected that the dominant neutralizing substances in the two samples are similar. This material can be deduced by comparing Carbonate standard curve of standard neutralizing material. The Carbonate standard curve is the curve obtained by performing ABCC experiments on known standard carbonate minerals. The following ABCC test examples are shown as 1 to 5.

[ABCC Test Example]

1. A sample of 75 μm or less (200 or less) is accurately weighed to the weight determined by ANC concentration, placed in a 250 ml Erlenmeyer flask, and 100 ml of distilled water is added.

2. Titrate until the target pH is reached or ANC equivalent is administered based on the HCl concentration and dose determined according to the ANC value, as shown in Table 6 below. When the HCl is added at the same time, make sure that the reaction reaches equilibrium with sufficient agitation for more than 1,000 seconds.

[Table 6]

3. Calculate the total amount of HCl injected in kg H ₂ SO ₄ / t units using the formula below.

4. Draw a graph with H ₂ SO ₄ / t as x-axis and 'pH' as y-axis.

5. Each kg H ₂ SO ₄ / t value of the Carbonate standard curve is multiplied by ANC 'of the ANC / carbonate standard of the sample so that it can be directly compared with the standard curve and ABCC of the sample.

cf) It is recommended to use the Carbonate standard curve obtained directly when conducting the experiment. In addition, the HCl concentration and dose used to obtain the Carbonate standard curve can be directly compared with the HCl value when the ABCC of the sample is obtained.

-Modified NAG (third test step)

In the course of NAG experiments, organic acids may be generated if the carbonaceous materials are forcibly oxidized by hydrogen peroxide. These organic acids are reflected in the NAG and NAGpH values and may eventually influence the acid production rate by NAG experiments. However, these organic acids are acids that are not related to the acids generated by the sulfide minerals and do not occur in the natural state, so they should be excluded from the NAG calculation. Modified NAG is an experiment in which NAG experiments are improved in view of the fact that these organic acids decompose under strong oxidizing conditions.

Modified NAG experiments are the process of oxidizing and decomposing all of the organic acids generated by adding strong hydrogen peroxide solution (adding more hydrogen peroxide and heating above boiling point) to the filtrate of the turbid solution after the NAG test. There are two methods (Extended NAG and Calculated NAG) for determining the acidity of the samples subjected to Modified NAG experiments and the method should be chosen according to the characteristics of the samples.

Extended NAG is a method of determining acidity by performing titration on samples that have undergone additional oxidation. This has the advantage of eliminating organic acids when calculating the acidity, but it has the disadvantage that part of the acid caused by the sulfide minerals can be decomposed. In addition, if some samples remain in the solution, the sulfide minerals in the sample may generate acid during the additional oxidation process. Therefore, the filtration process must be performed.

Calculated NAG is a method to estimate the acidity and acid neutralization ability by performing ion analysis on the solution after NAG experiment. The acidity is calculated by measuring the concentration of sulfur dissolved in the sulfide minerals and sulfate minerals present in the solution. In this case, the sulfate minerals do not affect the acid generation but are reflected in acid neutralization ability at the equivalent ratio of sulfur dissolved in the sulfate minerals (ex: CaSO ₄ = Ca ²⁺ (reflected in acid neutralization ability) + SO ₄ ^2- Reflected in performance) offset each other).

- scattering ability =

= The acid neutralization capacity is expressed by the following formula.

- Calculated NAG = acidity - acid neutralization ability

Generally, when sulfurized minerals and organic matter are present at the same time, hydrogen peroxide is more reactive with sulfide minerals than organic matter. In the presence of more than 0.7% of sulfide minerals, hydrogen peroxide is decomposed by heat of reaction between sulfurized minerals and hydrogen peroxide, so the probability of organic acids is low. It is also known that organic acids generally occur in samples with a total organic carbon (TOC) of 7% or more. Therefore, organic acids are more likely to form in samples with low sulfide mineral content (<0.7%) and high organic carbon (> 7%), and samples from coal mines generally meet these conditions.

As described above, the evaluation step is performed after the first to third test steps in the precision evaluation step. That is, evaluation is made to evaluate whether or not an acid of the sample is generated using the results of the first to third test steps. The difference between the acid neutralization ability of the result of the first test step and the result of the second test step of the sample is determined as the first acid generation amount and the result of the first acid generation amount and the third test step After the second acid production amount is set as the X axis and the Y axis, the sample corresponding to the first quadrant formed by the X axis and the Y axis is the acid generation sample, and the sample corresponding to the second quadrant and the fourth quadrant is the uncertainty sample , And the third quartile shall be evaluated and determined as the source of acid rain.

The present inventors conducted an experiment to determine the difference between the results obtained by the conventional test method and the test method according to the present invention.

- Existing Total S test vs Sulfur species analysis

First, 13 samples were tested by the KCl extraction method, which is an existing Total S test and a substitution test in the present invention. The results are shown in Table 7 below.

[Table 7]

Based on the data in [Table 7], the results of the comparison of the acid production amount obtained by using the existing method (calculated by the total sulfur content) and the improvement method (calculation by considering the sulfur species) are shown in FIG. As a result, in the case of the sample carried out by the method according to the present invention, it was confirmed that the generated acid was mostly formed by the sulfide and the amount of acid generated by the sulfate was very small compared to the amount of acid generated by the sulfide I could. The amount of acid generated by the improvement method in most of the samples was similar to the amount of acid produced by the conventional method, and it was confirmed that the content of sulfur in the samples was not large. However, in some samples (A2, B2, C1, C3), it is somewhat overestimated by calculating the amount of acid production by the existing method which assumes total sulfur content as pyrite. Therefore, it is necessary to evaluate sulfur species in order to accurately determine acid production.

- Existing ANC test vs ABCC test

FIG. 8 shows the result of applying the existing method (ANC) and the improvement method (ABCC) to the sample in order to evaluate the neutralization ability of the sample. As a result, the neutralization ability obtained through ANC in most samples except A1, A2, and D3 is the neutralization ability obtained through ABCC (the available ANC means a neutralizing ability that can react immediately when acid occurs) Which is significantly higher than that of This means that if the neutralization ability is evaluated through the conventional method, it can be seriously overestimated, which means that there is room for judging that the sample does not generate acid even though it is a sample which actually generates acid.

The reason for the difference in the results in the two test methods is that the ANC reacts the sample in a strong acid at about pH 1, but in contrast, the ABCC continuously injects acid into the acid, This is an experiment in which a strong acid is not allowed to react directly with the sample with a sufficient reaction time. In addition, the available ANC determined by ABCC is capable of neutralizing until it decreases to pH 4.0, so it can only react with highly soluble and highly reactive neutralized minerals such as carbonate minerals. On the other hand, the neutralization substances that can be eluted through ANC are various other than carbonate minerals. Biotite, chlorite, amphibole and olivine can be eluted during ANC and reflected in the result. However, these minerals are minerals that do not contribute to the actual neutralization ability because the sulfide minerals and soluble acid-generating sulfate minerals are considerably slower than the rate of acid generation in actual sites.

In order to examine the reason why the difference between ANC and ABCC is large, C2, C4, and D3 were selected considering ABCC / ANC ratio, and three conditions (33 = 9, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) analysis were performed. In the FT-IR data shown in Fig. 9, a peak was found at a wavelength of 874 cm &lt; ^-1 &gt; in D3, which was not found in C2 and C4 where ABCC values were small but ABCC was high. The peak at this wavelength was a typical peak of calcite (CaCO ₃ , Calcite), and the trend similar to ABCC results was confirmed. Also, it was confirmed that the calcite peak of D3 disappears through the reaction of ABCC and ANC.

XRD data and quantitative analysis results of C2, C4 and D3 samples are shown in FIG. 10 and [Table 8].

[Table 8]

The peak analysis was conducted with the aim of determining quantitatively reduced minerals due to ABCC or ANC reaction based on the peak before reaction among the XRD data. In particular, the minerals reacted with ABCC and ANC data were searched. As a result, it was confirmed that pyrrhotite and jarosite did not change during the ABCC reaction but disappeared through the ANC reaction.

In the above, we examined the cause of the difference of ANC and ABCC values by experimental method and surface analytical approach. Due to various causes (dissolution of non-carbonate minerals, dissolution of pyrrhotite and jarosite under acidic and anoxic conditions), ANC was found to have a much higher value than available ANC, which could neutralize the acid immediately. This difference in neutralization ability was found to be the biggest cause of errors in this study.

- Existing NAG test vs. Modified NAG test

The major cause of errors in the conventional NAG test is that the organic acid is generated in the sample and the NAG pH is measured low and the NAG value is measured to a large extent. However, in general, organic acids can not be produced in a natural state, and they are generated under forced oxidation conditions by hydrogen peroxide. This means that the organic acid generated during the NAG test should be excluded. Therefore, the most important factor in improving the NAG test is the separation of the acid generated by the sulfur and the acid generated by the organic matter (organic carbon and organic sulfur). As described above, the improvement method of the NAG test employed in the present invention is characterized in that additional organic acid after the NAG test is maintained at a temperature of 100 C or higher after the NAG test. The pH of the solution that has undergone the reaction under strong oxidizing conditions is called Extended NAG pH.

FIG. 11 shows a graph of a comparison between NAG pH and Extended NAG pH. Except for D3, which is used as a control group as a strong alkali sample, the difference between the two values is not large in most samples. However, it was confirmed that Extended NAG pH slightly increased in B1 and B2 samples. This is the result of decomposition of the organic acid during the Extended NAG test. The difference between B1 and B2 is that the carbon content is particularly high because the two samples are from coal mining. Stewart (2005) experimentally confirmed that the effect of organic acids is greater when 0.7% or less of sulfide minerals and 5% or more of organic carbon are present. In this experiment, the fact that the organic carbon of B1 and B2 samples were not measured directly but the total carbon content was about 20% could be an indirect clue that there is an influence of organic acids.

NAG, extended NAG, and calculated NAG are shown in Fig. 12 below to select the factors required for calculating the actual amount of acid production. The extended NAG value was found to be smaller than the NAG value in most samples. This is similar to the previous study in which sulfuric acid produced by the oxidation of sulfide minerals can be decomposed with organic matter under strong oxidizing conditions. The calculated NAG value is relatively high accuracy compared to the NAG value calculated by the titration method which may cause error according to the skill of the experimenter. However, since it is highly dependent on the concentration of dissolved sulfur in the solution, It is necessary to make a decision through appropriate judgment. The NAG value and the calculated NAG value in this experiment showed various tendency according to the samples but it was confirmed that the difference in value was not large.

As described above, the conventional methods for determining the generation of acid and the methods employed in the present invention are compared individually. Through various samples, it is found that in all experiments, there is a significant difference between the conventional method and the method employed in the present invention .

However, it can not be judged whether the experimental results obtained through the improvement measures of these different experimental results are really the result of actual acid production and the ability to represent the acidogenic ability. If the ABA test and the NAG test are ideal tests to determine the sporadic viability of the sample, then the indices (NAPP and NAG) derived by the two tests should be proportional. If the NAPP value or the NAG value of a sample shows a significant difference in the results, it can be judged that the test method did not properly evaluate the acidogenic ability of the sample. Therefore, if the improved test method can accurately judge the acid-generating ability of the sample compared to the conventional test method, the relationship between the two evaluation indexes should show a higher correlation.

The graphs of FIG. 13 and FIG. 14 show the relationship between the acid generation evaluation indexes obtained by the existing method and the improvement method. It can be seen that the correlation (R ² ) derived from the least squares method is increased from 0.8585 to 0.9712, which means that the estimation result of the acid generation by the improved method is more reasonable. Also, the ordinate axis in FIGS. 13 and 14 indicates that an acid is generated when the NAG value is 0 or more, and that no acid is generated when the NAG value is 0 or less, which generates an acid when the NAG pH is 4.5 or less. It is possible to think in connection with only the existing method and form which judge that it is not. Therefore, the results of judging whether or not the acid is generated in the sample can be clearly distinguished between the two methods. In FIG. 13, it can be seen that there are 10 samples in the region where the NAG value is equal to or greater than 0 and the NAPP is equal to or less than 0, which is the UC determination region showing the opposite result in the two indices. On the other hand, referring to FIG. 14, it can be seen that most of the NAPP and NAG are moved to a region of 0 or more, which is a region determined as PAF. In other words, not only the correlation between the two indices is improved through the newly proposed experimental method, but also the evaluation method according to the present invention is an alternative to overcome the limitations of the existing method since the samples judged as UC are re-evaluated as PAF .

The precision evaluation method proposed by the present invention is expected to be widely used in civil engineering work or abandoned mine area management, and is expected to be a standard for evaluation of acid occurrence.

For reference, it is noted that the terms "test" and "experiment" are used in this specification, and that a clear concept between them is not used separately at the academic level, so that the test and the experiment can be used in combination .

Claims (8)

To evaluate the acidity of rock samples,
A preliminary evaluation step of classifying the occurrence of the acid of the sample into an acid generation group, an acid rain generation group, and an uncertain group by ABA (Acid Base Accounting) test and NAG (Net Acid Generation) , A precision evaluation step is carried out for the sample which is determined as an uncertain group,
Wherein the precision evaluation step comprises:
A first test step of measuring the total amount of sulfide minerals composed of chemical species capable of generating acidic drainage through chemical species analysis of the sulfide minerals contained in the sample and converting the total amount of the sulfide minerals into the acidity of the sample;
A second test step of measuring the neutralization ability of the sample by applying the ABCC test method to the sample;
After the NAG test method was performed on the sample, the turbid solution was filtered through the NAG test method so as to exclude the influence of the organic acid generated in the NAG test method. Then, hydrogen peroxide was added thereto, heated to a temperature higher than the boiling point, A third test step of oxidatively decomposing the organic acid to measure the amount of acid generated in the sample; And
And evaluating the probability of occurrence of acid in the sample using the results of the first to third test steps. The method according to claim 1,
In the first test step, the total amount of the acid-generating sulfide and the acid-generating sulfate in the sulfide mineral was determined, and the total amount of the acid-generating sulfide and the acid-generating sulfate in the sample was determined as acidogenic sulfide, acid-generating sulfate, Of the total amount of mine waste. 3. The method of claim 2,
The KCl extraction method is used to measure the total amount of the acid-generating sulfate,
Characterized in that the CRS test is used to measure the total amount of the acid-generating sulfides. The method according to claim 1,
Wherein the titration is performed until the target pH is reached while repeatedly adding hydrochloric acid to the sample in the second test step, and stirring is performed at a reaction time of 1,000 seconds or longer when hydrochloric acid is once added, And a determination method. The method according to claim 1,
The measurement of the amount of acid generated in the sample in the third test step may be performed using an Extended NAG method in which the turbid solution after the oxidative decomposition of the organic acid is measured by titration or a Calculated NAG method in which the measurement is performed by ion analysis Determination and Determination Method of Mine Waste Acid Emission. delete The method according to claim 1,
In the evaluation step,
The difference between the acid neutralization ability of the acid value of the sample, which is the result of the first test step, and the result of the second test step,
The first acid generation amount and the second acid generation amount are set as the X axis and the Y axis, respectively, and then the sample corresponding to the first quadrant formed by the X axis and the Y axis is set as the acid generation sample Wherein the samples corresponding to the quadrants of the second quadrant and the fourth quadrant are evaluated as uncertainty samples and the samples corresponding to the quadrant of the third quadrant are evaluated and determined as samples of the acid rain. delete

Images