The Effects of Biochar on the Neutralization of Leachate in Acid Mine Drainage Sites
Ty MacGuffie, Cora Kilgo, Jerrica Crosby
Animas High School
A B S T R A C T
Acid mine drainage (AMD), also sometimes referred to as acid rock drainage, is the condition of acidic water flowing through mine tailings or other exposed rock. It is usually caused by metal or coalmines but also has happened in construction sites where rock is unearthed. Acid mine drainage has posed a threat to aquatic life and ecosystems in general and threatens the health of anything that uses the overly acidic water. The application of biochar, a carbon-intensive and very porous material, assists the retention of moisture and helps stimulate revegetation in the site. This plant growth will remove toxic metals from the soil and use them advantageously, causing the leachate pH to neutralize. At Animas High School, we experimented with the effectiveness of biochar on vegetation reinstatement with various samples from known AMD sites in the Silverton area using a plant growth trial. From our results we discovered that biochar does not necessarily promote vegetation reinstatement but this method of neutralization is certainly one that has proven itself effective. Our results also show a constant neutralization in the first week indifferent to Biochar concentration, telling that vegetation reinstatement is what made this difference.
1) Introduction
Acid mine drainage, also known as acid rock drainage, is the process in which elevated pH is caused by unintended exposure of metals and minerals in soil at mine sites or, in the case of acid rock drainage, turned over minerals in rock and soil in road and other commercial construction (Skousen, 1997). When toxic metals such as pyrite, the most commonly occurring metal that elevates pH in mine tailings, are exposed and leachate seeps through them, pH is elevated (Shackley, 2011). This is due to a series of reactions that result in the contribution of extra H+ ions, which increase acidity. Low pH can be very detrimental to aquatic life and other organisms, because an average ecosystem must have water with a pH around 7, considered neutral (Sophie, 2011).
Biochar, a charcoal created by pyrolysis of biomass, has a very porous structure with high surface area, allowing it to retain more water than soil (Reed, 2012). Extra moisture promotes plant growth allowing nutrients, phosphorous and agrochemicals to be retained by the plant for its own benefit and the plant sorbs toxic metals causing them to be not as present in the leachate, which flows into streams and other bodies of water (Solomon, 2009). Thus more vegetation will create a more neutral pH (Rennick, 2012).
2) Methods and Materials
In the growth trial experiment at Animas High School, students evaluated growth response of perennial vegetation to biochar amendments in mining affected soils. In preparation, different soils from various mine sites in the Silverton region (Bonner, Road Cut, Joe John, Across From Bonner, Brooklyn) were mixed with various concentrations of biochar. To carry out this experiment materials were initially collected (Soil samples, sieve, scale, biochar, volume measurement, grow lights, 3.5 inch containers w/ trays, mixing bowl, seed mixture, pH probe). The soil samples were set up by creating various accurate ratios of biochar and soil, adding a seed mixture (See Seed Mixture table), then filling the small plastic containers, and they were grouped by site and percentage. The ratios were 10, 20, and 30 percent by volume for each of the sites. Once all of the samples were set up they were placed under a grow light and set on a timed lighting sequence. Growth trials then began and students recorded various characteristics of the growth along with the pH of the leachate. The leachate pH’s were recorded in a chronological database by pouring 100ml of water through each soil sample, collecting the resulting water from all three trials with similar treatments and sites and then measuring the pH of the resulting leachate. We took pH samples with the Vernier LabQuest data collection device, always first calibrating the pH probe with both pH 7 and pH 10 solutions. The pH measurements were updated weekly for 55 days.
3) Results
From our experiment’s results, we can see no obvious or constant increase in pH with the use of biochar. The results show an erratic pattern and do not show a direct influence of biochar on pH of soil leachate. In each of the sites, both with high initial pH and low initial pH, the change in pH seems to have increased slightly throughout the experiment but not enough to deem it productive for the soil and the cause of acid mine drainage.
At AFB and RC sites, both with slightly higher initial leachate pH’s at 6.64 and 6.69, seemed to raise initially but then followed a generally random pattern. Both these sites’ pH’s were neutral at the end of the trial but the presence of biochar seemed not to affect this result.
At all other sites with slightly lower initial pH’s similar results were present. The pH rose most initially when the plants began to sprout but then changed somewhat erratically.
The presence of biochar in the samples seemed to affect them somewhat at different percentages but as a whole showed no direct obvious correlation, though at some sites for some samples there may have been more neutralization with a higher concentration of biochar.
4) Discussion
Our results have shown that the growth of the plants in our experiment neutralized the pH of the soil samples, though the data did not prove that biochar made a difference in the pH neutralization for the results seemed random or erratic. The various concentrations didn’t affect the leachate pH differently, and some showed lower leachate pH from the initial pH.
The initial rise in pH within the first week was constant throughout the samples so we can conclude that biochar was not responsible for this plant growth/neutralization. This was most likely due to the initial sprouting and growth of the plants that occurred within most samples.
Error also affected our results in the experiment and possibly could have invalidated them in whole. During the process of the experiment, the light that supported the plants was accidentally off, causing most of the vegetation to die. This prevented more metals from being removed from the soil and stopped any further neutralization that could’ve occurred.
These results should not be refuted though, for they still provide valuable evidence that proves the effectiveness of reinstating vegetation at an AMD site. Our results show that reinstating vegetation is an effective way to neutralize mine leachate, and that creating hospitable conditions for vegetation is the best start to a solution to AMD. Though there is an issue with vegetation reinstatement, getting plants to grow in highly acidic soil.
References
Skousen, J., Hilton, T., & Faulkner, B. (1997). Reclamation of Drastically Disturbed Lands. National Mine Land Reclamation, WV: WVU Extension Service. Retrieved May 6, 2012
Rennick, R. B. (2012). Hardrock Mining 2012. N.p.: United States EPA.
Sophie, U. (2011, December 8). Biochar Soil Amendment for Environmental and Agronomic Benefits. Retrieved May 6, 2012
Shackley, S., Carter, S., Sims, K., & Sohi, S. (2011, May 12). Expert Perceptions of the Role of Biochar as a Carbon Abatement Option with Ancillary Agronomic and Soil-Related Benefits. Retrieved May 6, 2012
Reed, D. What is Biochar? [Electronic version]. Biochar International.
Solomon, F. (2009, January). Impacts of Copper on Aquatic Ecosystems and Human Health. . Retrieved May 6, 2012
Acid mine drainage (AMD), also sometimes referred to as acid rock drainage, is the condition of acidic water flowing through mine tailings or other exposed rock. It is usually caused by metal or coalmines but also has happened in construction sites where rock is unearthed. Acid mine drainage has posed a threat to aquatic life and ecosystems in general and threatens the health of anything that uses the overly acidic water. The application of biochar, a carbon-intensive and very porous material, assists the retention of moisture and helps stimulate revegetation in the site. This plant growth will remove toxic metals from the soil and use them advantageously, causing the leachate pH to neutralize. At Animas High School, we experimented with the effectiveness of biochar on vegetation reinstatement with various samples from known AMD sites in the Silverton area using a plant growth trial. From our results we discovered that biochar does not necessarily promote vegetation reinstatement but this method of neutralization is certainly one that has proven itself effective. Our results also show a constant neutralization in the first week indifferent to Biochar concentration, telling that vegetation reinstatement is what made this difference.
1) Introduction
Acid mine drainage, also known as acid rock drainage, is the process in which elevated pH is caused by unintended exposure of metals and minerals in soil at mine sites or, in the case of acid rock drainage, turned over minerals in rock and soil in road and other commercial construction (Skousen, 1997). When toxic metals such as pyrite, the most commonly occurring metal that elevates pH in mine tailings, are exposed and leachate seeps through them, pH is elevated (Shackley, 2011). This is due to a series of reactions that result in the contribution of extra H+ ions, which increase acidity. Low pH can be very detrimental to aquatic life and other organisms, because an average ecosystem must have water with a pH around 7, considered neutral (Sophie, 2011).
Biochar, a charcoal created by pyrolysis of biomass, has a very porous structure with high surface area, allowing it to retain more water than soil (Reed, 2012). Extra moisture promotes plant growth allowing nutrients, phosphorous and agrochemicals to be retained by the plant for its own benefit and the plant sorbs toxic metals causing them to be not as present in the leachate, which flows into streams and other bodies of water (Solomon, 2009). Thus more vegetation will create a more neutral pH (Rennick, 2012).
2) Methods and Materials
In the growth trial experiment at Animas High School, students evaluated growth response of perennial vegetation to biochar amendments in mining affected soils. In preparation, different soils from various mine sites in the Silverton region (Bonner, Road Cut, Joe John, Across From Bonner, Brooklyn) were mixed with various concentrations of biochar. To carry out this experiment materials were initially collected (Soil samples, sieve, scale, biochar, volume measurement, grow lights, 3.5 inch containers w/ trays, mixing bowl, seed mixture, pH probe). The soil samples were set up by creating various accurate ratios of biochar and soil, adding a seed mixture (See Seed Mixture table), then filling the small plastic containers, and they were grouped by site and percentage. The ratios were 10, 20, and 30 percent by volume for each of the sites. Once all of the samples were set up they were placed under a grow light and set on a timed lighting sequence. Growth trials then began and students recorded various characteristics of the growth along with the pH of the leachate. The leachate pH’s were recorded in a chronological database by pouring 100ml of water through each soil sample, collecting the resulting water from all three trials with similar treatments and sites and then measuring the pH of the resulting leachate. We took pH samples with the Vernier LabQuest data collection device, always first calibrating the pH probe with both pH 7 and pH 10 solutions. The pH measurements were updated weekly for 55 days.
3) Results
From our experiment’s results, we can see no obvious or constant increase in pH with the use of biochar. The results show an erratic pattern and do not show a direct influence of biochar on pH of soil leachate. In each of the sites, both with high initial pH and low initial pH, the change in pH seems to have increased slightly throughout the experiment but not enough to deem it productive for the soil and the cause of acid mine drainage.
At AFB and RC sites, both with slightly higher initial leachate pH’s at 6.64 and 6.69, seemed to raise initially but then followed a generally random pattern. Both these sites’ pH’s were neutral at the end of the trial but the presence of biochar seemed not to affect this result.
At all other sites with slightly lower initial pH’s similar results were present. The pH rose most initially when the plants began to sprout but then changed somewhat erratically.
The presence of biochar in the samples seemed to affect them somewhat at different percentages but as a whole showed no direct obvious correlation, though at some sites for some samples there may have been more neutralization with a higher concentration of biochar.
4) Discussion
Our results have shown that the growth of the plants in our experiment neutralized the pH of the soil samples, though the data did not prove that biochar made a difference in the pH neutralization for the results seemed random or erratic. The various concentrations didn’t affect the leachate pH differently, and some showed lower leachate pH from the initial pH.
The initial rise in pH within the first week was constant throughout the samples so we can conclude that biochar was not responsible for this plant growth/neutralization. This was most likely due to the initial sprouting and growth of the plants that occurred within most samples.
Error also affected our results in the experiment and possibly could have invalidated them in whole. During the process of the experiment, the light that supported the plants was accidentally off, causing most of the vegetation to die. This prevented more metals from being removed from the soil and stopped any further neutralization that could’ve occurred.
These results should not be refuted though, for they still provide valuable evidence that proves the effectiveness of reinstating vegetation at an AMD site. Our results show that reinstating vegetation is an effective way to neutralize mine leachate, and that creating hospitable conditions for vegetation is the best start to a solution to AMD. Though there is an issue with vegetation reinstatement, getting plants to grow in highly acidic soil.
References
Skousen, J., Hilton, T., & Faulkner, B. (1997). Reclamation of Drastically Disturbed Lands. National Mine Land Reclamation, WV: WVU Extension Service. Retrieved May 6, 2012
Rennick, R. B. (2012). Hardrock Mining 2012. N.p.: United States EPA.
Sophie, U. (2011, December 8). Biochar Soil Amendment for Environmental and Agronomic Benefits. Retrieved May 6, 2012
Shackley, S., Carter, S., Sims, K., & Sohi, S. (2011, May 12). Expert Perceptions of the Role of Biochar as a Carbon Abatement Option with Ancillary Agronomic and Soil-Related Benefits. Retrieved May 6, 2012
Reed, D. What is Biochar? [Electronic version]. Biochar International.
Solomon, F. (2009, January). Impacts of Copper on Aquatic Ecosystems and Human Health. . Retrieved May 6, 2012
Field trip to Silverton, Rock on
This was a field trip my Chemistry class took to find soil samples to improve the ground where it has been mined away. I learned mostly how to get dirt from the ground. This is an ongoing lab because we havent done much with the samples yet but we will soon!
Letter to Nalgene
Dear Libba and Caroline,
I am a student at Animas High School in Durango, Colorado; I am writing in regards to your Bisphenol A(BPA) free Nalgene water bottles. In 2008, the media issued reports questioning BPA’s safety and therefore all of the bottles were changed to BPA free water bottles. I have recently had the problem of my water bottles breaking. I have done research on this subject and I have come to the conclusion that the key reason for why the water bottles a breaking is because the water bottles are BPA free.
Bisphenol A (BPA), is a chemical building block that is used primarily to make polycarbonate plastic and epoxy resins. The chemical was removed from all of the water bottles because of the concern for the health of the users. Polycarbonate plastic is a lightweight, high performance plastic that possesses a unique balance of toughness, and relatively low heath issues. I am suggesting that instead of removing the BPA, keep using the plastic that contains BPA so that the bottles are not as breakable but line the inside of the water bottles with the BPA free substance to minimize health concerns.
People, including myself have been complaining about the fact that your water bottles break easier now that they don’t have BPA in them. I hope that these suggestions are taken into consideration, and thank you for your time. Please contact me at [email protected]. I look forward to hearing about how you plan to resolve this issue.
Sincerely,
Cora Kilgo
Animas High School
3206 Main Ave
Durango, CO 81301
I am a student at Animas High School in Durango, Colorado; I am writing in regards to your Bisphenol A(BPA) free Nalgene water bottles. In 2008, the media issued reports questioning BPA’s safety and therefore all of the bottles were changed to BPA free water bottles. I have recently had the problem of my water bottles breaking. I have done research on this subject and I have come to the conclusion that the key reason for why the water bottles a breaking is because the water bottles are BPA free.
Bisphenol A (BPA), is a chemical building block that is used primarily to make polycarbonate plastic and epoxy resins. The chemical was removed from all of the water bottles because of the concern for the health of the users. Polycarbonate plastic is a lightweight, high performance plastic that possesses a unique balance of toughness, and relatively low heath issues. I am suggesting that instead of removing the BPA, keep using the plastic that contains BPA so that the bottles are not as breakable but line the inside of the water bottles with the BPA free substance to minimize health concerns.
People, including myself have been complaining about the fact that your water bottles break easier now that they don’t have BPA in them. I hope that these suggestions are taken into consideration, and thank you for your time. Please contact me at [email protected]. I look forward to hearing about how you plan to resolve this issue.
Sincerely,
Cora Kilgo
Animas High School
3206 Main Ave
Durango, CO 81301
This was a project that we did for Chemistry. The project included finding something that you wanted to fix and fix it then send it to the company that owned your object. For my project, I thought that BPA free water bottles were more breakable and my idea was to just line the inside of a water bottle with the BPA free substance and keep the outside just normal with BPA so that it doesn't break as easily. In this letter, I probably could have included more about Bisphenol. The hardest part of this project for me was actually finding something that I wanted to change. This was a good project in the sense that we had to interact with the real world and do most of it on our own.