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Industrial Wastewater Treatment
Published in Subhash Verma, Varinder S. Kanwar, Siby John, Environmental Engineering, 2022
Subhash Verma, Varinder S. Kanwar, Siby John
Hexavalent chromium is toxic (0.1mg/l threshold limit) and is present in tanning, electroplating, fertilizer production and other industries. Methods for the removal of chromium include: Cr6 is reduced to Cr3 by the addition of sulphuric acid (to reduce the pH to between 2 and 3) and ferrous sulphate. It is then precipitated in a settling tank after being neutralized with sodium hydroxide or calcium hydroxide.Cationic resins can be used to recover chromium in the form of sodium chromate or chromic acid. The regeneration of resin is done with sodium chloride and sulphuric acid.Lime coagulation and adsorption with activated carbon.Reverse osmosis.
Biopolymer Composites and Nanocomposites for Corrosion Protection of Industrial Metal Substrates
Published in Hatem M.A. Amin, Ahmed Galal, Corrosion Protection of Metals and Alloys Using Graphene and Biopolymer Based Nanocomposites, 2021
Saviour A. Umoren, Moses M. Solomon
Corrosion, commonly defined as the deterioration of a material (usually a metal) or its properties because of a reaction with its environment, is a global problem. NACE International, The Corrosion Society, estimates that global corrosion and its consequences cost developed nations about 3–5% of GDP or GNP [1]. Methods commonly employed to combat corrosion include cathodic protection, materials selection, coatings and linings and corrosion inhibitors. Corrosion inhibitors form a layer over the metallic substrate and protect the metal from corrosion, thereby enhancing the life of the metal. Coatings designed for corrosion protection must offer an effective physical barrier, impeding the access of aggressive species to the metallic interface. For many years, the most effective corrosion protection systems were based on the use of chromate-rich surface treatments and/or primers and pigments based on chromates [2]. However, the current legislation imposed by REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) prohibits the use of hexavalent chromium in almost all sectors except the aerospace industry [3]. Many alternatives have been explored so far, including a wide range of “green” surface treatments and pretreatments, environmentally safe pigments and natural corrosion inhibitors [4]. The latest developments propose coatings with low volatile organic compounds (VOCs), based on waterborne formulations and isocyanate-free compositions, as well as smart and self-healing polymers [4].
Bioremediation
Published in Mritunjoy Sengupta, Environmental Impacts of Mining, 2021
Hexavalent chromium is frequently targeted for chemical or electrochemical reduction to reduce its toxicity and mobility. Biological mechanisms can reduce Cr(V1) by direct microbial action or by microbial production of sulfide.
Parametric and Rate Studies of Reduction of Cr(VI) in Slurry of Contaminated Soil with Hydrazine and Sonochemical Augmentation
Published in Soil and Sediment Contamination: An International Journal, 2020
Gottemukkala Narsimha, Sudarsan Neogi, Binay K. Dutta
Soil and groundwater contamination by hexavalent chromium is a major environmental problem worldwide. Hexavalent chromium is considered a priority pollutant by USEPA under the Comprehensive Environmental Response, Compensation and Liability Act (USEPA 1993). Cr(VI)-contaminated sites exist in countries such as South Africa, Kazakhstan, Zimbabwe, Turkey, USA, Finland and India. In a recent survey of contaminated sites in India, 320 ‘probably contaminated sites’ were identified among which 111 sites have chromium contamination (MoEFCC 2015). Metallurgical, electroplating, production of paints and pigments, leather tanning, wood preservation, production of chrome chemicals, ferrous and nonferrous alloys, and refractories are major sources of chromium release into the environment through illegal dumping or unscientific waste disposal (ATSDR 2012; Li et al. 2017). Hexavalent chromium is a known human carcinogen and is phytotoxic. Cr(VI) in soil and groundwater can easily get into the living world and humans directly and indirectly. Thus, it is essential to decontaminate the soil in such areas in order to prevent its harmful impact on public health and the ecosystem.
Cr(VI) adsorption on low-cost activated carbon developed from grape marc-vinasse mixture
Published in Particulate Science and Technology, 2020
Hasan Arslanoğlu, Semih Kaya, Fikret Tümen
In aqueous solutions, chromium commonly exists in two stable oxidation states, Cr(III) and Cr(VI), which have different characteristics. Trivalent chromium is considered to be a trace element essential for the proper functioning of living organisms and it is toxic at high concentrations. Hexavalent chromium is known to be toxic and carcinogenic, affecting immune, urinary and respiratory systems and causing various illness and cancers. The USEPA has a drinking water standard of 100 μg/L for total chromium, which includes all forms of chromium including Cr(VI)(USEPA 2012). According to European regulations (Anonymous 1980), the maximum concentration of total chromium in drinking water was set as 50 μg/L. Accordingly, chromium, especially Cr (VI), should be regarded as a dangerous contaminant and remedies for its removal from water must be explored.
Effect of ventilation velocity on hexavalent chromium and isocyanate exposures in aircraft paint spraying
Published in Journal of Occupational and Environmental Hygiene, 2018
James Bennett, David Marlow, Fariba Nourian, James Breay, Amy Feng, Mark Methner
National Institute for Occupational Safety and Health (NIOSH) researchers investigated ventilation system performance in military aircraft paint finishing hangars as a function of air velocity delivered by the system to the work area. Previous investigations at the subject facility found exposures to isocyanates and hexavalent chromium exceeded occupational exposure limits (OELs).[1] Isocyanates are respiratory sensitizers and have health effects in both monomeric and oligomeric forms.[2–5] Hexavalent chromium exposure can cause nasal irritation and damage, and respiratory cancer, among other conditions.[6]