Boron Separation Processes

Nalan Kabay, Marek Bryjak, Nidal Hilal, Nalan Kabay, Marek Bryjak, Nidal Hilal

• Editore: Elsevier
• Anno: 2015
• ISBN:
  9780444634658
• Argomento: Technik & Maschinenbau
• Categoria: Chemie- & Biochemietechnik

The impending crisis posed by water stress and poor sanitation represents one of greatest human challenges for the 21 st century, and membrane technology has emerged as a serious contender to confront the crisis. Yet, whilst there are countless texts on wastewater treatment and on membrane technologies, none address the boron problem and separation processes for boron elimination. Boron Separation Processes fills this gap and provides a unique and single source that highlights the growing and competitive importance of these processes. For the first time, the reader is able to see in one reference work the state-of-the-art research in this rapidly growing field. The book focuses on four main areas:

• Effect of boron on humans and plants
• Separation of boron by ion exchange and adsorption processes
• Separation of boron by membrane processes
• Simulation and optimization studies for boron separation

• Provides in one source a state-of-the-art overview of this compelling area
• Reviews the environmental impact of boron before introducing emerging boron separation processes
• Includes simulation and optimization studies for boron separation processes
• Describes boron separation processes applicable to specific sources, such as seawater, geothermal water and wastewater

Chapter 1

Boron in the Environment

Fyodor S. Kot Faculty of Civil and Environmental Engineering, Technion–Israel Institute of Technology, Haifa, Israel

Abstract

In this introductory chapter, an up-to-date overview of boron (B) environment chemistry and biogeochemistry is given. The separate parts cover B concentrations, forms and turnover in the atmosphere, natural waters and bottom sediments, soils, microbiota, plants, animals, and humans. The role of natural organic matter in B binding and transformations, often unappreciated, is accentuated. Boron toxicology and medical geology/geochemistry are also considered.

Keywords

Atmosphere; Availability; Biota; Boron; Environment; Medical geology/geochemistry; Natural waters; Soil; Speciation; Toxicology

1.1. Boron History, Sources, Chemistry, and Applications

Boron (B) as an individual chemical element was first isolated in 1808 by Joseph-Louis Gay-Lussac and Louis-Jacques Thénard in France and, independently, by Sir Humphry Davy in England. In fact, neither had produced the pure element, which is almost impossible to obtain owing to its high melting point (about 3400 K). Eventually, Weintraub in the USA produced totally pure B by sparking a mixture of B chloride and hydrogen.¹ The material of B obtained in this way was found to have very different properties to those previously reported, described originally by Laubengayer et al.²

In spite of its small atomic weight B is much scarcer in space than H, He, and C. In chondrites, content of B was found to vary from 0.5 to 1.4 mg/kg.³ Deficiency of B in space caused its relative deficiency in the earth less than 1 mg/kg in the upper mantle. However, the element is enriched in the lithosphere—about 10 mg/kg in the continental crust and in seawater there is 4.5 mg/kg. In the earth's crust, B accumulates mostly in granitoides and pegmatites. Due to volatility of its compounds, B is a noticeable element in volcanic activity; B compounds are emitted to the atmosphere, they accumulate in the thermal waters and enter groundwaters. Boron endogenic ores relate to postmagmatic processes—skarn, forming borosilicates—datolite (CaBSiO₄OH) and borate-ludvigite ((Mg,Fe)Fe(BO₃)O₂).⁴

Boron is the only nonmetal in Group 13 of the Mendeleev Periodic Table and it has many similarities to its close neighbor carbon and its diagonal relative silicon. Thus, like C and Si, B shows a marked propensity to form covalent molecular compounds, but it sharply differs from them as it has one less valence electron than the number of valence orbitals. This is referred to as an “electron deficiency,” and has a dominant effect on the behavior of B in chemical processes. Elements of this type usually adopt metallic bonding, but the small size and high ionization energies of B result in covalent rather than metallic bonding. Boron normally has a coordination number of either three or four in naturally occurring compounds.

Free elemental B does not exist in nature. The most important oxidation state is B³⁺. The small highly polarizing B³⁺ cation does not exist under chemically significant conditions. When it comes about B in rocks, it is almost always about B complexes with oxygen. Ordinary exceptions to this generalization are ferrucite (NaBF₄), avogadrite ((K,Cs)BF₄), and barberiite (NH₄BF₄), which have been reported from Mount Vesuvius, Italy.⁵ Borates, such as boric acid, boric oxide, and sodium borates are stable, except for under dehydration at high temperatures.⁶

Boron is unique among elements in structural complexity of its allotropic modifications. It is second only to carbon in its ability to form element bonded networks. Vast numbers of organic compounds containing B–O are known.⁷ The B atom can be surrounded by innumerable combinations of groups, including acytoxy (RCOO–), peroxo (ROO–), halogeno (X–), and hydrido, in either open or cyclic arrays.^8,9 Simple alcohols react with boric acid to give esters B(OR)₃. The partially esterified species (RO)₂BOH and ROB(OH)₂ are probably also involved. Polyhydric alcohols form cyclic esters with boric acid.¹⁰ Organoboron compounds include B–N compounds, because B–N is isoelectronic with C–C.^11,12 Organoboron complexes occur in plants and are most likely present in animal and human tissues. Experimental evidence suggests these organoboron complexes are the result of interaction with either –OH or –NH₂ groups.¹³ The stability of B–N complexes of biological relevance remains to be shown. Thioborates of the type B(SR)₃, R′B(SR)₂, and R′₂(SR) are well documented.^8,14 There are also a growing number of binary B sulfides and B–sulfur anions, which may form chains, rings, and networks.⁸ Comprehensive reviews of known and probable natural B-containing compounds may be found elsewhere.^8,13,15–17

Boron compounds have been utilized since the early times.¹⁵ The Babylonians have been credited with importing borax (tinkar) over 4000 years ago for use as a flux for working gold. Mummifying, medicinal, and metallurgic applications of B are sometimes attributed to the ancient Egyptians. None of this very old borax history has been verified, but solid evidence exists that borax was first used in the eighth century in Hejaz, western Arabia having been brought there by Arab traders. The use of borax flux by European goldsmiths dates to about the twelfth century. The earliest source of borax was from lakes in Tibet. The borax was transported in bags tied to sheep, which were driven over the Himalayas to India.

In modern times, B compounds are widely utilized in indus...