Research Terms
Corrosion
This device continuously dewaters phosphatic clay suspensions through electrokinetics. A typical Florida phosphate mining operation produces more than 100,000 gallons per minute of phosphatic clay, which is pumped into large ponds known as clay settling areas, or CSAs. The current separation method of this mining waste product uses gravity settling and vast amounts of land. More than 150 squre miles of CSAs currently cover central Florida, representing 30 percent of the mined land. Consolidation of the clay can take 25 years to complete and still leaves clay too soft to build upon. The need both to reduce the land area required for clay suspension storage and to reduce the water usage in the mining operations has led researchers to search for an inexpensive method that can enhance the process of dewatering.
Researchers at the University of Florida have created a device that effectively separates water from phosophate mine clay solids and by applying an electric field. This design creates a 10-fold reduction in the electrode area, as compared to previous designs, which reduces efficiency and the cost to perform the continuous electrokinetic dewatering process. By utilizing electrical fields, this system also eliminates the need for chemical additives to aid the separation process, unlike its competitors.
An electrokinetic dewatering system for extracting water from phosphatic clay suspensions.
This device continually dewaters phosphatic clay using an electrokinetic method. It feeds phosphatic clay suspensions between two conveyor belts and allows the clay to come into contact with electrodes that apply an electric field. As it passes the electrodes, water drains freely away from the phosphatic clay solids and forms a dewatered cake solid, or thickened layer of clay, with a solids content of 31-38 weight percent, surpassing available dewatering methods. Additionally, this system allows for a 10-fold reduction in the required electrode area compared to a previous design, improving clay-water separation efficiency and reducing the operational cost, making this the ideal system for dewatering of phosphate mine tailings.
This sensor uses electrochemical impedance spectroscopy to detect corrosion in bridges and buildings supported by post-tensioned structural tendons. The Federal Highway Administration has rated nearly one in nine U.S. bridges as structurally deficient. With the average age of the nation’s more than 600,000 bridges at 42, bridge refurbishment costs upwards of $13 billion each year. Post-tensioned construction, common in bridges, has been a concern since cable corrosion caused bridges and buildings to collapse in the 1980s. Cable used in post-tensioned bridges usually consists of multiple strands of steel encased in a plastic sleeve. That plastic sleeve is filled with grout to protect the steel from corrosion; however, factors such as faulty grouting, inadequate waterproofing, and air voids can prevent the grout from protecting the wire strands. The loss or weakening of just a few wires could compromise the structural integrity. Available techniques including magnetic flux, ground-penetrating radar, impact echo, ultrasonic sound waves, and gamma-ray spectroscopy have been used to detect defects such as air voids or loss of steel due to corrosion. The results of these tests were not very accurate and were difficult to interpret. University of Florida researchers have developed an effective device. This sensor uses non-destructive, electrochemical impedance spectroscopy to detect corrosion in post-tensioned construction.
Sensor to detect corrosion in post-tensioned bridges and buildings
The sensor developed by UF researchers uses electrochemical impedance spectroscopy to detect regions in which corrosion has compromised the strength of the supporting cables. Inspectors drill holes into the protective plastic duct covering so that sensors can be placed in the holes, providing data without damaging the internal cables. By sending a sinusoidal current of different frequencies through the post-tensioned structure, the device can detect properties of the steel. A sinusoidal perturbation is applied at the grout surface and the potential response is measured to determine if corrosion or the conditions that might cause corrosion are present.
Continuous operation of this electrokinetic dewatering system removes water from phosphatic clay suspensions, thereby achieving clay cake solid contents approaching 25 percent more rapidly than other methods. In Central Florida, the quantity of clay settling ponds covers more than 150 square miles, taking up approximately 40 percent of the phosphate mining land mass. Drying these clay settling ponds requires decades, and even then the clay remains too soft to build upon. Both the need to reduce the land area required for clay suspension storage and water usage in the mining operations has spurred the search for enhancing solids-liquid separation. Researchers at the University of Florida have developed a method that applies an electric field to slurries, thereby greatly enhancing the removal of water from the phosphatic clay. This process speeds up the separation of water and clay solids without the use of chemicals. This important attribute will allow potential future technologies the ability to more effectively recover the residual phosphate entrained in the clay matrix.
An electrokinetic dewatering system for extracting water from phosphatic clay suspensions more quickly than traditional gravity settling alone
The electrokinetic dewatering system includes a continuous slurry influent flow, a region for cake formation and cake dewatering, electrodes, and conveyor belts. Subjected to a uniform electric field, the dispersed particles in the influent migrate toward the conveying belt, where they form a layer of thickened clay or cake before being transferred to the cake dewatering zone, where water is further removed via electro-osmosis. The cake continues to thicken to a solids content of more than 25 weight percent and can then be collected for further drying and/or disposal. The separated water can be clarified and recycled to the beneficiation plant.
