Abstract The reaction between rare earth oxychloride (REOCl) and water was investigated. X-ray diffractometer, volumetric titrations, FTIR spectrograph and scanning electron microscope were used to determine the reaction process and the reaction products. It was found that the reaction could be concluded as follows: 5REOCl(s) + 5H 2 O(l) = 2RE 2 (OH) 5 Cl(s) + RE 3+ (aq) + 3Cl − (aq). Based on this reaction, a new method for determining the purity of anhydrous rare earth chloride was proposed. Compared with the conventional method, the maximum absolute error decreased from 22 to < 1% and the maximum relative error decreased from 111 to < 4% under the experimental conditions. Graphic abstract
The Langmuir isotherm model is widely used for modeling adsorption equilibrium data. The linearization method is mostly applied for estimations of the Langmuir parameters. However, it is not unified and requires further study. In this paper, the applicability and accuracy of four linearization methods of the Langmuir isotherm (equilibrium adsorbate concentration ( C e )/equilibrium adsorption capacity ( q e )- C e , 1/ q e -1/ C e , q e - q e / C e and q e / C e - q e ) in parameter estimations by linear least squares regression (LSR) were compared. The influence of linearization on the assumption about errors in the LSR variables was analyzed. The results showed that Langmuir-1 ( C e / q e - C e ) and Langmuir-4 ( q e / C e - q e ) followed the assumption for all evaluated conditions whereas Langmuir-3 ( q e - q e / C e ) violated the assumption for all conditions. Langmuir-2 (1/ q e -1/ C e ) obeyed the assumption of LSR only when C e approached the initial adsorbate concentration ( C 0 ). Langmuir-1 ( C e / q e - C e ) provided the most accurate estimations of the Langmuir parameters, particularly at low levels of random errors in C e and when the errors (%) in estimated maximum adsorption capacity ( q m ) and constant ( K a ) ranged from −5% to 5% and from −15% to 15% at low levels of errors (−0.5–0.5 mg/L), respectively. The Langmuir-1 isotherm model adequately represented the experimental equilibrium data of sulfamethoxazole (SMX) onto activated carbon with an R 2 value of 0.96.
The reason for the prominent error in the hydroxyl radical detection method by UV-vis spectrophotometry with fast blue BB salt (FBBs) as the chromogenic agent was detected, and a modified method was proposed. The simultaneous extraction of FBBs in the diazosulfone extraction process was proven to have a distinct influence on the test results. In the modified method, FeSO4 was adopted to limit the extraction of FBBs by a toluene/butanol extraction agent, which sharply decreased the influence of FBBs on diazosulfone detection. The FBBs amount and extraction time played an important role in its extraction. The appropriate FBBs/MSIA ratio was 50, and the reasonable extraction time was 300 s for the modified method. ˙OH concentration in the directional decomposition of the Fenton system was detected. The test error was about 7%. This method is quite significant to test ˙OH quantificationally to better understand Fenton reaction mechanisms and promote the generation of ˙OH.
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