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Subsurface Processes
Published in Stephen M. Testa, Geological Aspects of Hazardous Waste Management, 2020
Broadly speaking, a buffer is any solid, species, reaction, etc. that tends to reduce or prevent a change within the system. Buffer is often used with respect to acid/base systems in which an acid/base reaction is controlled or buffered by some aspect of the system. Antacid tablets use the dissolution of various solids, such as CaCO3, MgOH, or Al(OH)3, to buffer the acidity of the stomach. CO32- or OH− from the dissolution reactions combine with H+, removing excess H+ as a new equilibrium is reached in the stomach. Nonchemical buffers also occur, exemplified by the melting of ice which buffers the temperature in a glass of water so that it remains at 0°C as long as ice remains in contact with the liquid.
An efficient technique for the purification of fulvic acid extracted from leonardite
Published in Chemical Engineering Communications, 2023
Md. Zahidul Islam, Aynur Manzak, Yasemin Yıldız, Yavuz Derin, Raşit F. Yılmaz, M. Shahinuzzaman, Ahmet Tutar
The molecular structure and origin of humic substances have been extensively studied over the past two centuries. The major constituents of humic substances (HAs and FAs) are produced from natural sources through a series of processes over thousands of years at a specific temperature and pressure. Humic and fulvic acids can be extracted from natural sources in various ways. In general, FAs and HAs are extracted from naturally occurring humic raw materials by sequential alkalization and acidification. Therefore, alkalization extracts humic and fulvic acids together, and acidification helps to separate humic acids from fulvic acids. Further crude products are washed with water to remove salts produced by acid-base reaction. FAs isolation in high yields is difficult because they are soluble in both acidic and basic mediums. Additionally, acidic solutions of fulvic acids contain undesirable materials derived from other acid-soluble particles or sources of humic substances. Sources of humic substances may also contain radioactive compounds related to fulvic acids, raising further concerns about the large-scale use of FAs. Moreover, FAs and HAs molecules have nearly identical polar functional groups, which introduce complexity for their separation and purification. Therefore, the purification of fulvic acids as natural compounds becomes more critical for their use in pharmaceutical and industrial sectors.
The study on interactions between stabilizers and asphaltenes
Published in Journal of Dispersion Science and Technology, 2022
Qingxuan Zhang, Yingjie Liu, Zengmin Lun, Jinhe Liu, Yuhui Zhang, Pujiang Yang
A small change in the O 1 s on the asphaltene surface but a significant change in N1s were observed after S1 (SDBS) was adsorbed on the asphaltene surface. Pyridine and pyrrole groups disappeared, and protonated pyridine N+ and pyridine nitrogen oxide - R-N+-O- were generated. The S 2p subpeaks indicated the presence of sulfonic acid at 168.5 eV and sulfonate at 169.7 eV, respectively. The sulfonic group 49% and sulfonic radical 35% suggested that there were two adsorption modes of S1 on asphaltene: acid-base interactions between sulfonic acid groups and asphaltene’s basic groups (pyridines and pyrroles), and π-π interactions between the benzene ring of S1 and polycyclic aromatics of asphaltene. This was consistent with the prediction of vertical adsorption (acid-base interaction) and the tiled arrangement (π-π interaction) of S1 on the asphaltene surface, as shown in Figure 4. Protonated pyridine and pyridine nitrogen oxides were produced by the acid-base reaction. The peak intensity of hydroxyls, esters, and carboxylic acids decreased from 40% to 21%, and the intensity of C = O and S = O increased from 18% to 38%, which may be because π-π interactions caused alkanes to cover the hydroxyl, ester, and carboxylic acid groups of asphaltene and exposed the sulfonic groups of S1.
Multiphase phosphate cements from steel slags
Published in Journal of Sustainable Cement-Based Materials, 2022
Carlos Andrés Cárdenas Balaguera, Maryory Astrid Gómez Botero
Some compounds are not identified by XRD, but are assumed to form part of the slag-based phosphate cements. These are the amorphous phases, mainly composed of amorphous iron phosphate, amorphous silica, and amorphous calcium phosphates. Some authors have identified the formation of amorphous silica and amorphous calcium phosphates (ACP) Cax(PO4)y.nH2O, from the acid-base reaction of wollastonite and aqueous phosphoric acid solution [7,9,32,33]. The main characteristic in the FTIR spectra for the amorphous calcium phosphate (ACP) corresponds to (V1) for PO4, the band identified as a shoulder at 950 cm−1 [34], which is visible for all the cements synthesized. The corresponding band at 868 cm−1, associated with the HPO42− ion, is also assigned to ACP [35]. The amorphous silica can be described by the Si – O – Si vibration, which is associated with short-tailed linear siloxanes, with a band at 1050 cm−1 [36] that is present in all the cements formed.