Chloride Removal Efficiency Research Articles

Development of a biological mercury removal-recovery system

A mercury removal-recovery system was developed for collection of elemental mercury volatilized by biological mercuric ion reduction. Using the mercury removal-recovery system, removal of mercuric chloride from mercury-containing buffer without nutrients by resting cells of mercury-resistant bacterium, Pseudomonas putida PpY101/pSR134 was tested. Optimum temperature, pH, thiol compounds and cell concentration on removal of mercuric chloride were determined, and 92 to 98% of 40 mg Hg l−1 was recovered in 24 h. The efficiency of mercuric chloride removal from river water and seawater was as high as that observed when using a buffered solution.

Chloride Removal by Intermittent Cathodic Protection Applied to Reinforced Concrete in the Tidal Zone

A basis for protecting steel in concrete using intermittent cathodic protection (CP) is provided by the removal of chloride ions from the surface of the steel. The present study reported on parallel, experimental, and theoretical investigations undertaken to study chloride removal effects induced by an intermittent CP current in a tidal zone situation. Factors that affected the short-term chloride removal efficiency included the resistivity of concrete, charge passed, treatment duration, initial chloride content, concrete cover, and chloride diffusion coefficient. Very high extraction efficiencies initially were observed sometimes, possibly as the result of pressure-induced flow of the pore solution resulting from the generation of gas at the cathode. Chloride removal appeared to be limited by the rate of release of bound chloride within the period of treatment if a high charge was applied in a limited period of time. However, in the long term, the chloride profile reached a steady state governed only by the concentration gradients and the average applied electric field determined by the charge passed in a given time and the resistivity. This may be used to select the steady-state design current density.

建設材料 デサリネーション適用後の鉄筋防食効果に関する研究

Desalination is one of the electrochemical methods, aiming to remove chlorides from reinforced concrete structures. However, it is impossible to extract all of chlorides contained in concrete. For this reason, it is important to improve the chloride removal efficiency and to estimate the durability of structures after treatment.In this study, distribution of Cl- (total chlorides and water soluble chlorides) was examined after applying desalination. The effect of discontinuous treatment was also investigated. Secondly, change of half cell potential and polarization resistance with time were measured after desalination.The results showed that the steel protection effect due to applying desalination had been maintained for long time. However, in this study, it was difficult to improve chloride removal efficiency by means of intermittent treatment. So, measuring of half cell potential and polarization resistance is useful to monitor the steel condition after treatment.

Electrochemical chloride removal from concrete prisms containing chloride penetrated from sea water

Electrochemical chloride removal tests were carried out in the laboratory of reinforced concrete prisms containing chloride due to 16 years' submersion in the North Sea. After 39 days of treatment using current densities of about 1 and 4 A/m2 steel surface, about 40% to 70% of the initial chloride was removed from the concrete on average. The chloride contents close to the rebars were reduced by 70 to 90% of the initial values. Less than 1% or 0.5% chloride by mass of cement remained around the steel after treatment at 1 or 4 A/m2, respectively. Steel potentials in treated specimens showed a strong shift towards more positive values, indicating passivation, while potentials in control specimens remained strongly negative, corresponding to active corrosion. No influence on the chloride removal efficiency was found from the electrolyte type, the cement type or the water-to-cement ratio. The removal efficiencies were relatively high, corresponding to high chloride ion transport numbers in the pore solution and suggesting quick release of bound chloride. Good overall agreement was found between the removed amounts of chloride determined from chloride in the concrete and from chloride accumulated in the electrolyte. Microscopic examination showed that the number of microcracks had increased slightly in some specimens, probably due to build-up of hydrogen gas pressure.

The electrochemical removal of chlorides from reinforced concrete

Results of a 2-year field study performed in Switzerland to evaluate the process and to obtain information on the efficiency of electrochemical chloride removal as a restoration technique for chloride contaminated concrete are presented. It is shown that about 50% of the initial chloride content is removed within 8 weeks ( ca 5 × 10 6 C m −2). In the treated zones of the structure the half-cell potentials became more positive by about 80–100 mV. A comparison with the theoretical efficiency for chloride removal, calculated from the transference number of chloride ions, show that mainly the free chlorides in the pore solution of the concrete are removed. Due to the slow chemical equilibrium between bound and free chlorides, a second treatment after several months also removes originally bound chlorides. For severe and inhomogeneous chloride contamination local zones with active rebars and high chloride content may remain after the treatment.