10/11/2023 0 Comments Chromate chromium chargeChromium has been shown to exist in aqueous systems in the form of oxyanions such as hydrogen chromate (HCrO 4 −), chromate (CrO 4 2−), and dichromate (Cr 2O 7 2−), depending on the pH of the solution. Moreover, chromium species can cause serious diseases, such as lung cancer, nasal irritation, nasal ulcers, hypersensitivity reactions, and contact dermatitis. For example, the high concentration of chromium in the ecosystem inhibits the growth of plants by preventing the absorption of nutrients. However, the presence of chromium in ecosystems or environments has triggered severe problems for animals and human beings. Thus, it was confirmed that the LDH–BT prepared by solid-phase hybridization is a practical clay-based nanocomposite for in situ soil and groundwater remediation.Ĭhromium (Cr) has been used in various industries, such as electroplating, dyeing, cement production, mining, photography, etc. Furthermore, when the LDH–BT_SP was injected into a box container filled with silica sand to simulate subsurface soil conditions, the chromate removal efficacy was around 43% in 170 min. The mobility of the as-prepared LDH–BT_SP was investigated on a silica sand-filled column to demonstrate that the mobility of the bentonite is dramatically decreased after hybridization with LDH. The results of the isotherm experiments were well fitted with the Langmuir and Freundlich isotherm model and demonstrate multilayer chromate adsorption by the heterogeneous LDH–BT_SP, with a homogenous distribution of LDH nanoparticles. The chromate adsorption by the LDH–BT_SP was performed under various concentrations (isotherm) and contact times (kinetic). The effect of varying the LDH amount in the LDH–BT composite was further investigated, and a positive relationship between the LDH ratio and chromate removal efficiency was identified. Among the composites, the LDH–BT_SP was found to exhibit the highest chromate removal efficiency of 65.7%. The chromate adsorption efficacies of the pristine materials (LDH and bentonite) and the as-prepared nanocomposites were investigated. The prepared LDH–BT nanocomposites were preliminarily characterized by using powder X-ray diffractometry, scanning electron microscopy, and zeta-potentiometry. The color of these ions is pH dependent, as indicated by the color changes when the above reactions take place.Herein, magnesium/aluminum-layered double hydroxide (MgAl-LDH) and bentonite (BT) nanocomposites (LDH–BT) were prepared by co-precipitation (CP), exfoliation–reassembly (ER), and simple solid-phase hybridization (SP). If a shift in pH causes the solution to become more acidic (i.e. The equilibrium equation can be represented byīy Le Chatelier’s Principle, if certain conditions (concentration, temperature, pressure, volume, etc.) are changed, the amount of each ion present in solution is affected. I will try to take a different approach to your question (in terms of acidity and basicity).Ĭhromate (yellow) and dichromate (orange) ion are at equilibrium in solution. The complementary color of blue is red slash orange, and that is in fact the color we see in the dichromate ion!Īt the heart of all this is the principle that the colors we see are those wavelengths of light which on average are not absorbed by a large number (on the order of Avogadro's number) of molecules.Īn approach like this will only be reliable for very similar molecules like the two we have here. That means, if one of the bonds in the chromate ion, and thus two of the bonds in the dichromate ion, were absorbing a longer wavelength like we said earlier, on average we would expect something just longer than purple-ish, like blue, to be absorbed. Thus, in the case of the chromate ion, we see yellow, and across from yellow is the purple-ish region. Now to the color wheel! It is a general chemistry (often unexplained) fact that the color we see is the complementary color of the wavelength of a bond's vibration. This means that bond will vibrate at a lower frequency, and because frequency and wavelength are inversely related, that bond will absorb a longer wavelength of light. If you look at the structure of the chromate and dichromate ions next to each other (see here for structures: ), the only major difference between the two is that the Cr-O bond joining the two chromate ions (missing an oxygen) is now a single bond. I'm really excited for this because I get to reference the almighty color wheel!! Fair warning, this answer is much more qualitative than quantitative, but that's more interesting sometimes anyways.
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