Date of Graduation
Bachelor of Science in Chemical Engineering
Penney, W. Roy
Committee Member/Second Reader
The process of mining minerals and elements from ores and rocks creates acid rock drainage (ARD). This drainage is water that contains heavy metals and minerals that can be dangerous for human consumption or damaging to the environment. The mining industry has employed various water treatment methods to prevent these metals and minerals from being discharged into water sources such as ponds, lakes, and streams. Currently, the most used treatment process in the mining industry is a cost-effective high-density sludge (HDS) process. This method reduces the concentration of metals and elements with the use of lime/limestone. However, the concentration of fluoride is not reduced to Environmental Protection Agency (EPA) standards, and so it is necessary to design a fluoride removal system. Reverse osmosis (RO) was considered as well as precipitation, ion exchange, and adsorption by media such as biochars, bone char, and activated alumina. Although RO is perhaps the most obvious solution to reducing fluoride concentrations, this method was eliminated due to expensive overhead and maintenance costs. Many metals and compounds present in the mine water will lead to severe scaling and precipitates collecting in the membrane, requiring constant upkeep and high maintenance costs. Precipitation was eliminated because it produced a byproduct only suitable for landfilling, and ion exchange was eliminated due to its high cost and complications with competitive ions. Adsorption was chosen as a viable option for fluoride removal because of its low cost and environmentally friendly byproduct generation. The adsorption media was chosen based on a ranking system designed by our team. This system provided a way for our team to compare the adsorption capacity, rate of adsorption, byproduct application, and price per ton for each adsorbent. From this ranking system, Moo Pig Sooie is presenting a solution of cow bone char as a fluoride adsorbent. This type of biochar can be bought pre-charred and can be land applied as a fertilizer once the char is spent. A full-scale facility was designed to treat 1000 gallons per minute (GPM) of mine water 24 hours a day, seven days a week, for eight months out of the year. To achieve this flowrate and timeline, two packed beds with volumes of 8,900 ft3 each were designed to run in parallel to ensure loading does not occur until the 168-hour mark, the end of the work week. Once the bone char is loaded, the spent bone char will be hauled offsite to be land applied in soil that is naturally slightly acidic. Our experimental results indicate that minimal amounts of fluoride are stripped from bone char in acidic environments. Applying spent bone char to soil presented a desirable environmentally friendly solution for our byproduct. The overall capital cost of a full-scale facility is approximately $750,894 with a yearly operating cost of $4,778,840. Although this is high, the proposed solution will reduce the concentration of fluoride to EPA standards of 2ppm and the process will generate a land-applicable byproduct. Since consuming fluoride in excessive amounts can lead to health issues, public awareness is a necessary aspect of this solution. Citizens affected by the application of fluoride to their soil and water sources should be regularly involved in and aware of the fluoride levels in their environment. From our analysis of bone char adsorption, Moo Pig Sooie believes this type of treatment is a beneficial, cost effective, and sustainable solution for mining facilities that generate high concentrations of fluoride in their water.
adsorption, fluoride, bone char, biochar, water treatment, soil amendment
Phan, E., Damian, A., Le, K., Johnson, M., Golman, C., Dopp, M., & Payne, J. (2020). Removal of Fluoride from Mine Water via Adsorption for Land-Applied Soil Amendment. Chemical Engineering Undergraduate Honors Theses Retrieved from https://scholarworks.uark.edu/cheguht/161