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Environmental Aspects of Sodium Borohydride
Using NaBH4 as a reducing agent makes it possible to solve ecological problems
The Intrinsic reduction ability of sodium borohydride is a driving force of many fundamental chemical transformations. This low-cost inorganic material has found application in various industrial processes, like removal/recovery of metals (by reduction of ores or waste), bleaching of paper and pulp (primarily liquid NaBH4, which also contains caustic), recycling of cellulosic materials, chemical reduction of nitro-aromatics and coal water slurry desulfurization, etc. All these processes can severely impact numerous environmental challenges, and sodium borohydride is one of the critical tools that help find innovative solutions. Some good examples are given.
Metal removal/recovery. Recovery of precious and heavy metals from wastewater is critically essential for protecting the environment. The relatively high costs and technical difficulties in removing trace precious metals from wastewater generated from the refining process of precious metals, makes this a subject of significant importance. The reduction potential of NaBH4 helps to recover metals like Ag, Pt, Pd, Au, Fe and Cu from strongly acidic aqueous solutions [1-3].
Several treatment methods such as precipitation, adsorption, ion-exchange and membrane technologies have been developed for metal remediation [2]. Precipitation is the mostly widely used of these methods because it is the most economical method and easier to implement and operate on a large scale. However, traditional precipitation methods using lime, sulfides or hydroxides recover metals in the form of a sludge that is not reusable and has to be disposed of in landfills creating a potential environmental hazard and resulting in loss of valuable minerals. Due to the fast depletion of mineral reserves globally, the current focus in effluent treatment is now on the recovery and re-use of these heavy metals rather than removal and disposal. A good example of the reductive precipitation of Cu in its elemental form using NaBH4 as a reductant has been reported in detail [2].
Another powerful application feature of NaBH4 is the chemical redox degradation of nitroaromatics and their derivatives. Nitroaromatics consisting of benzene rings with nitro (–NO2), hydroxyl (–OH) and (–NH2) groups, are widely used in the synthesis of dye, plasticizer, pesticide, herbicide, paint, pharmaceuticals, explosives and wood or leather preservatives. Some compounds have high toxicity, carcinogenicity, and bioaccumulation [5-6]. In the reduction process of nitrophenols to aminophenols NaBH4 is used with precious metal catalysts [5-6]. However, low cost pristine annealed Co3O4 where oxygen vacancies are formed in aqueous solution of NaBH4 acts as a remarkably effective catalyst [5] as well. A critical comprehensive review discusses the chemical reduction of nitroanilines using sodium borohydride [7]. The chemical reduction of nitroanilines using sodium borohydride is discussed in a key comprehensive review [7]. The removal of Congo red dye from aqueous solutions by a catalytic reduction using sodium borohydride in the presence of various inorganic nano-catalysts has also been reviewed [8].
An ever-growing exploitation and utilization of fossil fuels leads to an increasing atmospheric concentration of carbon dioxide. For example, sodium borohydride has been used in an innovative method for CO2 absorption from coal-fired flue gas under atmospheric pressure and using moderate temperatures [9].
VENPURE™ sodium borohydrides are available in the Strem Catalog in several modifications:
11-1117 VENPURE™ AF CAPLETS (sodium borohydride), min. 99%
11-1119 VENPURE™ SF GRANULE (sodium borohydride), min. 98.5%
93-1118 VENPURE™ SF POWDER (sodium borohydride), min. 98.5%
11-1120 VENPURE™AF GRANULE (sodium borohydride), min. 99%
11-1121 VENPURE™ SOLUTION (sodium borohydride 12%; sodium hydroxide 40%)
References:
- Mater. Trans. 2011, 52, 1462.
- IOP Conf. Ser. Earth Environ. Sci. 2018, 120, 012022.
- Minerals, 2021, 11, 673.
- RSC Advances, 2012, 2, 8867.
- Chem. Eng. J. 2019, 359, 13.
- ACS Omega, 2019, 4, 483.
- RSC Adv.2020, 10, 19041.
- J. Clean. Prod. 2018, 187, 296.
- Renew. Sustain. Energy Rev. 2016, 64, 84.
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