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Ground Water Remediation
Published in Paul N. Cheremisinoff, Handbook of Water and Wastewater Treatment Technology, 2019
Stripping is a unit operation of mass transfer which enhances the separation of volatile compounds from solution. The process exploits the difference between the actual concentration and the equilibrium concentration of the dissolved compounds (gases, vapors) in water. The basic concept in a stripping process is to provide a liquid-vapor interface, the point at which phase change occurs. The volatile compounds leave the liquid phase at the liquid surface. The rate of mass transfer depends on transfer area (interface surface area) and driving force (the concentration differential between liquid and vapor). Maximizing the overall separation can be achieved by increasing the interface surface area, increasing the mass flow rate through the system, and/or increasing the driving force.
Physical Processes
Published in Ralph L. Stephenson, James B. Blackburn, The Industrial Wastewater Systems Handbook, 2018
Ralph L. Stephenson, James B. Blackburn
Steam stripping consists of treating the contaminated stream of water in a packed vessel where the water is trickled down through the packing and steam is countercurrently forced up through the packing, or is generated by heating the VOC contaminated water. This system has been used in a number of cases for at source treatment of VOC contaminated industrial waste water and is also commonly used for sour water treatment. Since the process raises the water temperature to above the boiling point of most VOCs, effectively boiling them off, the process works very well, removing VOCs to extremely low levels in the water. In fact, the levels to which this process can remove VOCs are used as the basis of many regulatory requirements. The process generates a stream of VOC contaminated condensed steam, which must be properly disposed of. This can be accomplished by fractional condensation or by distilling the VOCs from the condensed steam or by burning the steam and VOCs in a boiler or furnace. Since the entire stream of water must be heated to steam temperatures, this process is usually used only for low volumes of contaminated wastewater, although the heat is usually recovered. VOCs can also be recovered from the fractional condensation or distillation process with carbon columns or with low temperature condensers, but again, the cost effectiveness of these methods is generally limited to smaller streams.
Produced Wastewater Treatment Technology
Published in Frank R. Spellman, Hydraulic Fracturing Wastewater, 2017
Air stripping is the process of transferring a contaminant from the liquid phase to the gas phase. In the air stripping process, air and water are contacted in a packed column designed to maximize the contact surface area between the water and air. Air stripping performance depends on such factors as the following: Characteristics of the volatile material (e.g., partial pressure, Henry’s constant, gas-transfer resistance) (AWWA, 2005)Water and ambient air temperatureTurbulence in gaseous and liquid phasesArea-to-volume ratioExposure time
Separation of phosphoric acid and magnesium from wet process phosphoric acid by solvent extraction
Published in Canadian Metallurgical Quarterly, 2022
Baoqi Wang, Qinglie Zhou, Chuan Chen, Haifeng Liu, Lin Yang
At present, the methods for purifying WPA mainly include solvent precipitation, crystallization, chemical precipitation, ion exchange and solvent extraction [4–7]. Solvent extraction is the most widely used method at present. Low energy consumption, high purity of purified phosphoric acid and large production capacity are the main advantages of the solvent extraction method. Extraction is currently the most suitable method for industrialisation WPA purification. The methods of extraction are divided into two concepts. The first method is extraction of phosphoric acid (H3PO4) from WPA, leaving impurity ions in residual acid. Alcohols [8], ethers [9], ketones [10,11], phospholipids [12], amines [13], and sulfite extractants [14] are common extractant that used for H3PO4 extractant. The second method is extraction of metal ions form WPA, such as Fe3+ [15–17], Al3+ [18], Mg2+ [19], and Zn2+ [20]. In fact, the extraction of metal ions in WPA can not only purify WPA, but also efficiently recover the associated resources in WPA. After extraction of metal ions, stripping is an indispensable process, which is vital for reuse of extractant and recovery of metals. However, efficient stripping of metal ions from extractant is an urgent problem to be solved. In previous reports, all the calcium, magnesium and aluminum ions in the extractant were stripped with a certain concentration of sulfuric acid, and then iron powder and sulfuric acid solution were used to reduce and strip out the iron ions, so as to realise the regeneration of the extractant [21,22]. The previous stripping process has problems such as difficulty in recycling the stripping liquid, and difficulty in separating the sulfuric acid solution containing magnesium and aluminum ions. Therefore, the cost of the entire process is increased, and it is difficult to realise industrialisation.