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The Acid Mine Drainage Problem from Coal Mines
Published in Mritunjoy Sengupta, Environmental Impacts of Mining, 2021
Excess carbon dioxide redissolves calcium to form calcium bicarbonate. Precipitates of calcium carbonate and metal hydroxide precipitates are removed by sand filtration. The resulting filtrate will have a pH of 10.3 and will contain about 35 mg/L of dissolved calcium carbonate at its minimum solubility level. Additional carbonation can reduce the pH to an acceptable level for potable water.
Water Quality Parameters
Published in Joseph Cotruvo, Drinking Water Quality and Contaminants Guidebook, 2019
Calcium and magnesium are commonly present in water as soluble bicarbonates that are formed when carbonates react with carbon dioxide. The bicarbonate, carbonate, carbon dioxide, and water are in equilibrium. Bicarbonate predominates in the pH range of about 6–10. Calcium bicarbonate is soluble at about 16.5 g/100 mL around room temperature, but calcium carbonate solubility is only about 0.0013 g/100 mL, so it is clear that it will precipitate when conditions favor its presence. Higher pH and heat cause loss of carbon dioxide and conversion of the bicarbonate to carbonate.
The Acid Mine Drainage Problem from Coal Mines
Published in M. Sengupta, Environmental Impacts of Mining, 2018
Excess carbon dioxide redissolves calcium to form calcium bicarbonate. Precipitates of calcium carbonate and metal hydroxide precipitates are removed by sand filtration. The resulting filtrate will have a pH of 10.3 and will contain about 35 mg/L of dissolved calcium carbonate at its minimum solubility level. Additional carbonation can reduce the pH to an acceptable level for potable water.
Research progress on scaling mechanism and anti-scaling technology of geothermal well system
Published in Journal of Dispersion Science and Technology, 2023
Huijun Zhao, Yahong Huang, Song Deng, Lei Wang, Haoping Peng, Xin Shen, Dingkun Ling, Lu Liu, Yuan Liu
CaCO3 scale is formed when the activity product of Ca2+ and in a fluid is greater than the equilibrium constant at the current temperature, usually associated with an increase in pH. According to the pH value of the solution required for the formation of scale, the types of scale can usually be divided into “alkaline scale” or “non-alkaline scale”. CaCO3 is a common type of alkaline scale formed by the decomposition of calcium bicarbonate and the increase in pH of the brine. Three major reasons account for the increase in pH of geothermal fluids, i.e., CO2 degassing due to high temperature boiling; corrosion of the metal casing and hydrogen precipitation reaction; and CO2 escape due to the intrusion of other insoluble gases such as nitrogen. All this will lead to an increase in the pH value and increase in pH of fluid encourages the conversion of bicarbonates () to carbonates (), resulting in forming calcium carbonate. In addition, when the geothermal fluid flows from the bottom of the well to the ground, the pressure decreases linearly, which will cause the solubility of calcium carbonate to decrease, and then will cause the formation of calcium scale.[35–37]
Utilization of by-pass cement kiln dust and air-cooled blast-furnace steel slag in the production of some “green” cement products
Published in HBRC Journal, 2018
Nour T. Abdel-Ghani, Hamdy A. El-Sayed, Amel A. El-Habak
It is worth mentioning that, in spite of the fact that, replacing 30% of the cement used in interlock paving units by CKD could yield products offering very reasonable properties, yet, it is recommended to keep the cement replacement ratio at the level of 20%. This is due to their utilization and location in actual service (pavements, side walls, road separators, etc.). So, they will be prone to weathering action (i.e. atmospheric air, humidity, water and CO2). This could lead to carbonation since CKD contains appreciable content of free lime (CaO) that will be transformed, by time, into CaCO3. This carbonate could react with atmospheric CO2 and water yielding soluble calcium bicarbonate:
Steel reinforcement corrosion in concrete – an overview of some fundamentals
Published in Corrosion Engineering, Science and Technology, 2020
The attack of buried concrete by carbon dioxide dissolved in the groundwater is a two-stage process. The calcium hydroxide solution that fills the pores of the concrete, first reacts with dissolved carbon dioxide to form insoluble calcium carbonate. However, it then subsequently reacts with further carbon dioxide to form soluble calcium bicarbonate which is leached from the concrete. The extent to which each process takes place is a function of the calcium carbonate/calcium bicarbonate concentration of the ground water (which in turn is a function of the pH and the calcium content) and the amount of dissolved carbon dioxide.