Water Self-Softening Processes at Waterfall Sites

Many rivers in tropical and subtropical karst regions are supersaturated with respect to CaCO3 and have high water hardness. After flowing through waterfall sites, river water is usually softened, accompanied by tufa formation, which is simply described as a result of water turbulence in fast-flowing water. In this paper, a series of laboratory experiments are designed to simulate the hydrological conditions at waterfall sites. The influences of air-water interface, water flow velocity, aeration and solid-water interface on water softening are compared and evaluated on a quantitative basis. The results show that the enhanced inorganic CO2 outgassing due to sudden hydrological changes occurring at waterfall sites is the principal cause of water softening at waterfall sites. Both air-water interface area and water flow velocity increase as a result of the 'aeration effect', 'low pressure effect' and 'jet-flow effect' at waterfall sites, which greatly accelerates CO2 outgassing and therefore makes natural waters become highly supersaturated with respect to CaCO3, consequently resulting in much CaCO3 deposition and reduction of water hardness. Aeration, rapidly increasing air-water interface area and water flow velocity, proves to be effective in reducing water hardness. This study may provide a cheap, safe and effective way to soften water.

Development of high quality Fe_3O_4/rGO composited electrode for low energy water treatment

Electrochemical water treatment is an attractive technology for water desalination and softening due to its low energy consumption. Especially, capacitive Deionization(CDI) is promising as a future technology for water treatment. Graphene(rGO) has been intensively studied for CDI electrode because of its advantages such as excellent electrical conductivity and high specific surface area. However, its 2D dimensional structure with small specific capacitance, high resistance between layers and hydrophobicity degrades ion adsorption efficiency. In this work, we successfully prepared uniformly dispersed Fe3O4/rGO nanocomposite by simple thermal reactions and applied it as effective electrodes for CDI. Iron oxides play a role in uniting graphene sheets, and specific capacitance and wettability of electrodes are improved significantly;hence CDI performances are enhanced. The hardness removal of Fe3O4/rGO nanocomposite electrodes can reach 4.3 mg/g at applied voltage of 1.5V, which is 3 times higher than that of separate r GO electrodes.Thus this material is a promising candidate for water softening technology.

The use of graphene oxide membranes for the softening of hard water

Strong chemical interactions between the oxygen-containing functional groups on graphene oxide(GO)sheets and the ions of divalent metals were exploited for the softening of hard water.GO membranes were prepared and evaluated for their ability to absorb Ca2+and Mg2+ions.These GO membranes can effectively absorb Ca2+ions from hard water;a 1 mg GO membrane can remove as much as 0.05 mg Ca2+ions.These GO membranes can be regenerated and used repeatedly.