Hydromagnesite (HM) is a widely distributed primary natural carbonate mineral . To expand the application range of hydromagnesite and tap its fire-extinguishing potential, a new type of high-efficiency KHCO 3 @HM dry powder was prepared by coating potassium bicarbonate on the surface of hydromagnesite with a dip coating method. KHCO 3 @HM dry powder obtained a chemical inhibition effect through this method, and the fire extinguishing efficiency has been further improved. A series of tests were carried out to confirm the excellent physical and chemical inhibition effect of KHCO 3 @HM dry powder. Specific surface area tests showed that the specific surface area of KHCO 3 @HM dry powder (31.405 m 2 /g) was higher than NH 4 H 2 PO 4 dry powder (12.766 m 2 /g). Flowability tests showed that KHCO 3 @HM dry powder (0.04 g/s) achieved the same flowability as NH 4 H 2 PO 4 dry powder (0.04 g/s). Local oil basin fire experiments showed that the average fire extinguishing time of KHCO 3 @HM dry powder was shorter with less powder consumption. Under 0.2 MPa driving pressure, the fire extinguishing time of KHCO 3 @HM dry powder was 2.2 s faster than NH 4 H 2 PO 4 dry powder, and the dry powder consumption was 3.71 g less than NH 4 H 2 PO 4 dry powder. The cooling effect of KHCO 3 @HM dry powder (208 ℃) in 10 s was better than NH 4 H 2 PO 4 dry powder (157 ℃), and KHCO 3 @HM dry powder (399 ppm) showed a better smoke suppression effect than NH 4 H 2 PO 4 dry powder (545 ppm). The pyrolysis of KHCO 3 @HM dry powder reduced the fire temperature, diluted the oxygen concentration, and captured free radicals. The final pyrolysis products formed a thick oxide film to provide good heat insulation and asphyxiation effects. The excellent cooling, dilution, asphyxiation, and chemical inhibition mechanisms of KHCO 3 @HM dry powder were demonstrated, and finally achieved a comprehensive performance comparable to NH 4 H 2 PO 4 dry powder.
Electrochemical precipitation is a promising technique for hardness abatement without the addition of external ions. However, the scale layer on cathode deteriorated the removal efficiency and limited the practical application. Herein, a fenced cathode structure was designed to prevent cathodic precipitation. The cathode was fenced by a crystallization-inducing material for separating the OH − production and crystallization processes. Precipitation on the cathode was confirmed to shift to the crystallization-inducing material, and the clean fenced cathode provided efficient long-term OH − production. At a current density of 40 A/m 2 , the Ca 2+ or Mg 2+ removal efficiency increased by 12.8% or 46.1%, respectively, compared to those of a traditional cathode. Thermodynamic equilibrium in synthetic water and mine water, mass transfer and the location of precipitation were analyzed to elucidate the electrochemical precipitation process. The enhanced mechanism was ascribed to the crystallization-inducing material, which remarkably promoted the crystallization process, and hindered OH − migration, thereby increased the pH of alkaline microenvironment. Notably, a recovery design was proposed to recover pure calcite and brucite from alkalinity-free wastewater. The design reveals a promising strategy for enhancing the crystallization process and reducing cathodic scale, also initiating a new research direction toward hardness removal.
Xudong Gong,Qiang Tian,Jiebiao Li,Ju Wang,Minhao Yan,Mark J. Henderson
Incorporation of fission products in spent nuclear fuel is of interest in the frame of safe storage of high-level nuclear waste in a deep geological repository. Uranyl oxyhydroxide films were grown on silicon wafer to represent the corrosion product formed on the surfaces of the fuel. Films were obtained by hydrolysis of uranyl ions (9 mM) in mild conditions (≤60 °C) using either Mg(OH) 2 , raw brucite, La(OH) 3 , or NH 4 OH to control the solution pH to ≈ 5.0. To identify the mineral phases we used the grazing-incidence X-ray technique. Atomic force microscopy data indicated that the surfaces of metaschoepite films prepared using either Mg(OH) 2 or brucite at 50 °C for 3 h were self-affine fractal ( D f = 2.5). The concentration (wt.%) of reactant ions detected in a metaschoepite film after reaction at 70 °C for three days as determined by X-ray fluorescence was: La (8.90) > Nd (5.6) > Ce (3.2) > Eu (2.5) > Pb (0.7) > Sr (0.14). Metaschoepite and sodium uranate hydrate were identified in a film formed in Cl-SO 4 -Na type groundwater from the Beishan area (China), the preselected area of a radioactive waste disposal repository.
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