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Halogen-Based FRs
Published in Asim Kumar Roy Choudhury, Flame Retardants for Textile Materials, 2020
Halogen-free flame retardants (Birnbaum and Staskal, 2004) cover a variety of chemicals which are commonly classified (PIN) as: Phosphorus-based flame retardants include organic and inorganic phosphates, phosphonates, and phosphinates, as well as red phosphorus, thus covering a wide range of phosphorus compounds with different oxidation states.Inorganic category comprises mainly metal hydroxides such as aluminum hydroxide and magnesium hydroxide. Other compounds such as zinc borate are used to a much smaller extent.Nitrogen-based flame retardants are typically melamine and melamine derivatives (e.g., melamine cyanurate, melamine polyphosphate, melem, melon). They are often used in combination with phosphorus-based flame retardants.Intumescent flame retardants are an example of a typical mechanism of halogen-free flame retardants. The combustible material is separated from the fire or heat source by an insulating foam forming at the surface. Intumescent flame retardant systems can be applied to decrease flammability of thermoplastic polymers, such as polyethylene, polypropylene, polyurethane, and polyester and epoxy resins.
Hydrometallurgical Waste Production and Utilization
Published in Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde, Waste Production and Utilization in the Metal Extraction Industry, 2017
Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde
In order for the hydroxide precipitation process to work effectively, enough hydroxide (OH−) ions must be supplied to raise the solution pH so that the dissolved metals can form insoluble metal hydroxides and settle out of the water. A variety of chemicals such as lime, caustic soda and limestone can be used to precipitate metal hydroxides from leach solutions and wastewater streams. A flocculant is added to the mixed slurry that is fed into a solid/liquid separation step. In most processes, a clarifier is used for solid/liquid separation, although a settling pond can also be used. Although widely used, hydroxide precipitation processes tend to generate large volumes of sludge, which can present dewatering and disposal problems (Kongsricharoern and Polprasert, 1996).
High Density Solids from Acid Wastewater Treatment
Published in Bell John W., Proceedings of the 44th Industrial Waste Conference May 9, 10, 11, 1989, 1990
A natural consequence of removing metals from waste acids is the generation of metal hydroxide. There is a need to minimize costs associated with the handling and disposal of these solid residues. Typically, the solids that are generated by conventional neutralization processes settle poorly and seldom attain solids concentrations greater than 5% upon gravity settling. At this concentration, 20 pounds of sludge must be discarded for each pound of solids generated. The reason for this gelatinous mass is the occurrence of excessive water-bonding on the surface of the particles in conventional processes, as illustrated (Figure 1).
Process variables that defined the phytofiltration efficiency of invasive macrophytes in aquatic system
Published in International Journal of Phytoremediation, 2023
Yetunde Irinyemi Bulu, Nurudeen Abiola Oladoja
In the sediment, at a low pH value range, competition between H+ ion and dissolved metals for ligands become intense, such that the metal adsorption reduced, and the mobility increased (Li et al.2013). Therefore, a higher release of metals occurs at a lower pH value range from sediment into the overlying water. The solubility of metal hydroxide minerals increases as the system pH value reduced, thereby increasing the bioavailability of metals. The uptake of ammonium () by plant roots releases a proton (H+) to the solution, which increase proton concentration around the roots, and a diminution in the pH value around the roots. The uptake of Nitrate () releases bicarbonate (), which also increase the pH value around the roots.
Advancements in laundry wastewater treatment for reuse: a review
Published in Journal of Environmental Science and Health, Part A, 2022
Sushil Kumar, Ali Khosravanipour Mostafazadeh, Lalit R. Kumar, R. D. Tyagi, Patrick Drogui, Emmanuel Brien
The pollutants like ions, organic colloids, and inorganic colloids are removed from various wastewater effluents by using electrocoagulation process (EC). During the treatment process wastewater passes through the EC cell and voltage is applied. At the anode electrode, EC delivers the coagulant in situ by anodic dissolution in wastewater subjected to treatment. At the cathode surface, water is reduced into hydrogen gas and hydroxyl ion. The dissolved metal ions (coagulating agents: Al3+ or Fe2+/Fe3+) then encounter suspended particles to neutralize the negative surface charge. The coagulating agents can also react with hydroxyl ions and produce iron (or aluminum) hydroxides having a considerable sorption capacity. These metal hydroxides can simultaneously remove suspended solids, heavy metals, and other pollutants by co-precipitation or complexation. Figure 3 shows the treatment mechanism of EC process.
The application of electrochemical processes in oily wastewater treatment: a review
Published in Journal of Environmental Science and Health, Part A, 2021
Morana Druskovic, Drazen Vouk, Hana Posavcic, Ivan Halkijevic, Karlo Nad
The essence of the electrochemical AOP and EC process in the reaction vessel (electrochemical reactor) relies on the influence of an electric field of sacrificial anodes which release metal cations (e.g. Fe2+, Al3+) necessary for the coagulation/flocculation of contaminants present in water are released from the electrodes. Simultaneously, water is ionized to hydrogen ions (H+) and hydroxide ions (OH-), at the cathode, while oxygen is released at the anode. Stable metal hydroxides are formed by the reaction of cations and OH- ions. Suspended and dissolved contaminants are removed by coagulation/flocculation with electrochemically generated metal cations and co-precipitation with metal hydroxides. The wastewater is mixed with electrochemically generated gases (H2, O2) (Fig. 1). Any toxic Cr6+ present is removed by electroreduction with electrochemically generated Fe2+ to form stable Cr3+, which is further removed from solution by precipitation in the form of a stable hydroxide. Electroreduction also reduces any nitrates and nitrites present to nitrogen gas.[33,34] All these processes occur according to the following reactions: