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Hydrometallurgy — An Introductory Appraisal
Published in C. K. Gupta, T. K. Mukherjee, Hydrometallurgy in Extraction Processes, 2019
The two fundamental parameters that hydrometallurgists can use to control the behavior of metals in aqueous solutions are pH and the oxidation potential of the solution. The thermodynamic behavior of an aqueous system is determined by these two parameters, together with the concentrations or activities of dissolved species. The pH of the solution, of course, determines the acid-base character of the system and is the main parameter controlling the solubility of oxidized or hydrolyzed metal species. A large number of hydrometallurgical processes are critically dependent on the control of pH for their successful operation. This control may be achieved by deliberately adding acid or base during a reaction to consume hydroxyl or hydrogen ions produced by the reaction or by designing the chemistry of the system so that it is self-buffering. An example is aluminum hydroxide. It is an amphoteric hydroxide and behaves as an acid. () Al(OH)3(s)⇄AlO(OH)2(aq)+H +(aq)
Basic Chemical Principles
Published in John A. Conkling, Christopher J. Mocella, Chemistry of Pyrotechnics, 2019
John A. Conkling, Christopher J. Mocella
There are several concepts and theories for acid–base reactions but the one most useful in pyrotechnics is Brønsted–Lowry acid–base theory, named after the scientists who independently developed the model. In this concept, an acid is commonly described as a molecule or ion that can serve as a hydrogen ion (H+) donor. The hydrogen ion is identical to the proton—it contains one proton in the nucleus and has no electrons surrounding the nucleus. H+ is a light, mobile, reactive species. A base is a species that functions as a hydrogen ion acceptor, such as a hydroxide ion, OH−. The transfer of a hydrogen ion (proton) from a good donor to a good acceptor is called an acid–base reaction. Materials that are neither acidic nor basic in nature are said to be neutral, while those that can act as both an acid and a base (such as water) are called amphoteric.
Household and Personal Care Products: Cleaning up and Looking Good
Published in Richard J. Sundberg, The Chemical Century, 2017
Surfactants are a component of most consumer products that involve cleaning, such as dishwashing and laundry detergents, shampoos and body soaps. Surfactant molecules are called amphipathic, meaning they can interact with both water (hydrophilic, polar) and nonpolar (hydrophobic, lipophilic) phases. The hydrophilic portions are charged or polar and interact favorably with water and are often called “head groups.” The hydrophobic portions are usually hydrocarbon chains of 8–20 carbons in length and are called the “tail.” All surfactants have a common mechanism of action. They reduce surface tension at phase boundaries, and thus permit formation of high surface area systems such as emulsions and foams. Surfactants can be classified as anionic, cationic, amphoteric, zwitterionic, or neutral, depending on their charge characteristics. Amphoteric compounds have both acidic and basic groups and their charge depends on the pH of the medium. Zwitterionic surfactants are neutral but have separate anionic and cationic sites. Neutral surfactants have no charge but have polar substituent groups. One example is short polyethylene glycol (PEG) chains. Other types of compounds that have a long chain and a polar functional group, including alcohols, amides, and amine oxides exhibit surfactant properties.
Fluoride removal from water using alumina and aluminum-based composites: A comprehensive review of progress
Published in Critical Reviews in Environmental Science and Technology, 2021
Sikpaam Issaka Alhassan, Lei Huang, Yingjie He, Lvji Yan, Bichao Wu, Haiying Wang
This section of the paper focused on the use of activated alumina (AA) and aluminum-based composites for adsorption of fluoride. The advantages of activation as well as some defects have also been highlighted and the mechanisms of adsorption and adsorption efficiency of various materials have been reviewed and compared. Activated alumina is a kind of aluminum oxide, semi-crystalline (Rabia et al., 2018) with surface area significantly over 200 m2·g−1 and mostly used as desiccant and sorbent for elements such as fluoride, arsenic and selenium in water. It has a high surface area to weight ratio due to its high porosity with amphoteric properties (Salvador et al., 2015). Its amphoteric nature allows it to behave as an acid in basic medium and as a base in acidic medium. Because of its high affinity, it is mostly a preferable desiccant for moisture removal from air as well as a catalyst in natural gas and refining operations. There are two common methods of activating Al2O3 thus, thermal treatment otherwise called physical activation and chemical treatment with acid in the laboratory.
Enhancement of protein flocculant properties through carboxyl group methylation and the relationship with protein structural changes
Published in Journal of Dispersion Science and Technology, 2021
Rafael A. Garcia, Phoebe X. Qi, Matthew Essandoh, Lorelie P. Bumanlag
Proteins are amphoteric biological polymers. When dosed into aqueous suspensions, some proteins will promote flocculation while others will not. The factors behind the differential flocculant activity are not yet well understood, but the charged side chains seem to play an important role. Bovine hemoglobin (BHb; pI = 6.8) from slaughterhouse blood has been demonstrated as an effective flocculant for suspensions of kaolin clay or lignin,[3–7] but its flocculant activity decreases rapidly for pH > 5.5. The pH range over which BHb flocculant activity drops seems to coincide with the loss of the positive charge on histidine residues (pKa = 6.04), rather than the transition of BHb’s net charge from positive to negative at the pI. Bovine serum albumin (BSA; pI = 4.8), also from slaughterhouse blood, has no flocculant activity against kaolin clay at pH 5.5.[7,8] Hen egg white lysozyme (HEWL; pI = 10.7) has been demonstrated to flocculate suspensions of kaolin, activated carbon, microalgae, and papermill biosludge.[9–11] HEWL’s flocculant activity seems to be unrelated to its catalytic activity, as thermally inactivated HEWL has flocculant activity very similar to native HEWL. Like BHb, HEWL’s flocculant activity occurs in a limited pH range; it showed good flocculant activity with kaolin suspensions at pH 5.1 and 7, but none at pH 3 or 9. This activity pattern isn’t clearly related to HEWL’s pI; hypothetically, the drop in activity between pH 5 and 3 could be related to protonation of aspartic acid and glutamic acid residues.
Study of adsorption characteristics of long chain alkyl amine and petroleum sulfonate on silicates by electrokinetic potential, microflotation, FTIR, and AFM analyses
Published in Particulate Science and Technology, 2019
Savaş Özün, M. Ümit Atalay, Şahinde Demirci
When mineral particles are brought into contact with aqueous solutions, ions on the mineral surfaces chemically bond to water molecules as a consequence of surface complexation. The hydroxyl groups on the mineral surfaces form pH base negatively or positively charged surface species through protonation or deprotonation (Churchill, Teng, and Hazen 2004). The hydrous oxides, such as Si–O and Al–O, display amphoteric structure which accepts or donates proton in aqueous solutions. The surface reactions where central metal ion is Si or Al can be given as below;