Ion concentration, classification science and chemistry,solutionContaining certain ionstotalAndvolumeThe ratio, expressed in n/V, is generally expressed in mol/L.
Add caustic soda solid (the volume change of solution can be ignored) to the solution containing the following ions, and what can cause the ion concentration to decrease?
A、HCOthree-；B、Cl-；C、OH-；D、Cutwo+；
Answer: Select AD
HCOthree-+OH-=HtwoO+COthree2-
Cutwo++2OH-=Cu(OH)two↓
HCOthree-、Cutwo+Both decrease, OH-Concentration increase, Cl-The concentration is almost constant.
Free ion concentration of heavy metals in soil
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The concentration of free ions of Cd, Zn, Pb and Cu in 11 cultivated layer soils collected from different regions of China was studied by using the Daonan membrane technology, a method to study the concentration of free ions of heavy metals.The results show that the free state concentrations of Cd and Zn measured by DOWNAN membrane technology are in good agreement with those calculated by WinHumicV model, and the free state concentrations of Pb and Cu measured by DOWNAN membrane technology are slightly higher than those calculated by WinHumicV model.At the same time, the adsorption model proposed by Sauv é was used to analyze dissolved and free heavy metals. The results showed that dissolved Zn, Cu and Pb as well as free Zn and Cu were controlled by the pollution degree of soil (total amount of heavy metals), soil pH and dissolved organic carbon in solution.[1]
Sample sampling and analysis
Take 10mL and 5mL samples from the supply solution and the receiving solution respectively after the system runs for 24, 36 and 48h.Determine the pH value of the sample.At the same time, the sample of the supplied liquid is 0.45μM filter membrane, and measure the concentration of dissolved organic carbon with TOC meter.After acidification with nitric acid, the remaining samples of the supply solution and the receiving solution are used to determine the concentration of various element ions. The elements K, Ca, Na and Mg are determined by ICP-OES, and the dissolved and free Cd, Zn, Pb and Cu concentrations are determined by ICP-MS (the dissolved heavy metal concentration refers to the supply solution Ca (NOthree)twoThe concentration of heavy metals in the medium, including free heavy metals and some bound heavy metalsCation exchange membraneFree heavy metals), using the formula proposed by Temminghoff et al.: [M2+]d=[M2+]a([K+]d[K+]a)twoCalculate the concentration of all free metal ions.Where [M2+]dIs the concentration of divalent free metal ions in the supplied solution;[M2+]aIs the concentration of divalent free metal ions in the receiving solution;[K+]dIs the potassium ion concentration in the supply solution;[K+]aIs the potassium ion concentration in the receiving solution (through K+To correct the ionic strength).[1]
Logarithmic determination of free state Cu and Pb
From the comparison between the logarithmic measurement results of free state Cu and Pb measurement values and the WinHumicV estimation results, it can be seen that the Cd measured by the Donnan membrane technology2+And Zn2+The free state concentration of is in good agreement with the results calculated by WinHumicV model, while Pb2+And Cu2+The free state concentration of is slightly higher than that calculated by the model.This result may be caused by the different influence of soil properties such as pH value and organic matter on the concentration of free ions of the above four heavy metals, such as free Pb2+And Cu2+And free state Cd2+And Zn2+In contrast, it is more affected by organic matter or soluble organic carbon in soil, which may lead to differences (Sauv é et al., 2000; Weng, 2001).
PH value and organic matter (or DOC) are two factors that have a greater impact on the speciation of heavy metals in soil solution.It can be seen that the regression equation of dissolved Zn in soil has a good fit (p=0.002) after considering pH of soil and total Zn in soil.If the variable log (SOM) is added to the equation, the regression equation fitting degree is good, but there is little difference from the fitting degree of only considering the pH of soil and the total Zn in soil. However, if the variable log DOC is added to the equation, the determination coefficient of the fitting equation increases by about 0.13~0.14, and the regression equation fitting degree is good,This indicates that the concentration of dissolved Zn in soil solution is controlled by soil pollution degree (total Zn content), soil pH and dissolved organic carbon in solution.Similarly, the concentration of dissolved Cu and Pb is also controlled by soil pollution degree (total amount of heavy metals), soil pH and dissolved organic carbon in solution, which is consistent with the research results of Sauv é et al. (2000).The main control factors of the concentration of free Zn and Cu in the soil are the same as the control factors of their dissolved concentration, which are also controlled by the pollution degree of the soil (total amount of heavy metals), soil pH and dissolved organic carbon in the solution.For free Pb in soil, even if the pollution degree of soil (total amount of heavy metals), soil pH and dissolved organic carbon in solution are taken into account, they cannot be accurately fitted, which indicates that the concentration of free Pb in soil may have other influencing factors.[1]
Review of critical chloride ion concentration in reinforcement corrosion
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Some key problems in the research methods of critical chloride concentration are summarized and analyzed, such as the expression form of critical chloride concentration, the determination method of chloride concentration, etc. The advantages and disadvantages of each research method are pointed out in order to provide reference for future research.[2]
Definition of critical chloride concentration
There are two main definitions of critical chloride concentration: one is the highest concentration of chloride ions in the concrete pore fluid around the reinforcement that will not cause the reinforcement to be passivated from the perspective of scientific research;The other is defined from the perspective of engineering practice as the concentration of chloride ions in the concrete pore fluid around the reinforcement when the reinforced concrete structure is deteriorated to a visible or acceptable degree.However, because it is difficult to quantify the visible or acceptable deterioration in the latter, leading to the increase in the dispersion of test results obtained by different researchers, researchers use the former more to define the critical chloride concentration.[2]
Expression of critical chloride concentration
The expression forms used in the study of critical chloride concentration are different, which is also an important factor for the large dispersion of critical chloride concentration.For example, Alonso and Sanchez have statistically collated a large number of critical chloride ion concentration values in the existing literature, and the critical chloride ion concentration range expressed by the percentage of total chloride ions in cementitious materials (520 data) is 0.3% to 4%;The critical chloride concentration range expressed by the percentage of free chloride ion in cementitious material (350 data) is 0.1% to 2.5%;Based on the molar concentration of free chloride ion andHydroxyl ionMolar concentration ratio [Cl－]/[OH－]The indicated (320 data) most critical chloride ion concentrations range from 1 to 3, but the total range is 0.2 to 20.It can be seen that the data obtained from various expression forms are quite discrete. Therefore, the expression forms of critical chloride concentration need to be summarized and classified. The main expression forms are summarized as follows:
(1) With free chloride ion content Cl－FreeExpressed as a percentage by weight of cement, cementitious material or concrete;
(2) With free chloride ion Cl－FreeConcentration vs. OH－Molar ratio of concentration;
(3) With free chloride ion Cl－FreeMolar concentration of, mol/L;
(4) Based on the total chloride ion content Cl－TotalExpressed as a percentage by weight of cement, cementitious material or concrete;
(5) Take the total chloride ion Cl－TotalConcentration vs. H+The molar ratio of the concentration.[2]
Characterized by free chloride ion concentration
Firstly, from the perspective of reinforcement corrosion mechanism, free chloride ion is the main cause of reinforcement corrosion, so free chloride ion is used to characterize the critical chloride ion concentration.
Through X-ray photoelectron spectroscopy andatomic force microscopeIt is found that the passivation film is a double-layer amorphous n-type semiconductor phase forming film, and its surface is very uneven;Through the study of X-ray photoelectron spectroscopy, it is believed that the film breaking mechanism is more likely to be that free chloride ions are adsorbed on the surface of the film first, and then a certain amount of free chloride ions penetrate into the film through the surface defects of the passive film, forming FeCl in the inner layer of the passive filmtwoSo that the passive film is locally dissolved and destroyed.From the perspective of the mechanism of chloride ion membrane breaking, free chloride ion is the main form of rebar corrosion－When a certain concentration is reached on the passive film on the reinforcement surface, and under other corrosion conditions (such as OtwoAnd HtwoO) The reinforcement will start to corrode when it is available;However, the bound chloride ions bound in the chloraluminate and absorbed by the CSH gel have lost their free state and will no longer react with the steel passive film. Therefore, the critical chloride ion concentration value should be expressed as the percentage of the free chloride ion concentration in the concrete void liquid in the weight of cement, cementitious materials or concrete.[2]
Method for determination of chloride ion concentration
In the study of critical chloride concentration, how to determine the chloride content in concrete is one of the key issues.Because the measurement methods adopted by different researchers are different, and the selection of measurement methods will directly affect the accuracy of the experimental results, which is also one of the main reasons for the large dispersion of the experimental results. Therefore, a general analysis should be made on the measurement methods of chloride ion concentration in order to facilitate subsequent experimental research and the formulation of unified experimental standards.The determination methods of free chloride ion and total chloride ion were summarized and analyzed.[2]
