Synthesis and Thermal Treatment of Lithium- and Magnesium-Containing Geopolymers

<p>Geopolymers are a class of cementitious aluminosilicate materials that are receiving an increasing amount of attention due to their potential applications in toxic waste remediation and as construction materials. They are composed of a network of crosslinked silicate and aluminate tetrahedra with charge-balancing alkali cations and are therefore similar in composition to alkali aluminosilicate zeolites. They are, however, x-ray amorphous.¹⁻⁴ They are formed by the dissolution of a solid aluminosilicate in a solution of alkali hydroxide or alkali silicate to form aluminosilicate ions which subsequently polymerise. The effects of adding magnesium to metakaolin geopolymer systems was examined. Magnesium was added as soluble magnesium salts and as magnesium oxide and hydroxide. When added as a soluble salt, an amorphous magnesium (alumino)silicate with a lower degree of silicate polymerisation than a geopolymer is formed. When added as the oxide or hydroxide, hydrotalcite is formed. In both cases, the product is produced alongside a separate geopolymer phase. A magnesiumcontaining geopolymer phase was not found in either. When heated to 1200°C, geopolymers with magnesium oxide added bloated to form lightweight foams. Lithium analogues of conventional metakaolin geopolymer systems with a range of lithium, aluminium, silicon and water contents were examined. Systems with molar ratios similar to those of commonly studied sodium and potassium metakaolin geopolymers produce self-pelletised lithium zeolites. The zeolite formed was Li-EDI, the lithium analogue of zeolite F. This is the first reported synthesis directly from metakaolin. True lithium geopolymers are found not to form in the systems examined. The zeolite bodies react to form β-eucryptite and β-spodumene at temperatures from 800 – 1350°C. The use of aluminium hydroxide and amorphoud silica rather than aluminosilicates as raw materials for the formation of potassium geopolymers was found to produce geopolymers with embedded grains of unreacted silica and aluminium hydroxide.</p>

Synthesis and Thermal Treatment of Lithium- and Magnesium-Containing Geopolymers

<p>Geopolymers are a class of cementitious aluminosilicate materials that are receiving an increasing amount of attention due to their potential applications in toxic waste remediation and as construction materials. They are composed of a network of crosslinked silicate and aluminate tetrahedra with charge-balancing alkali cations and are therefore similar in composition to alkali aluminosilicate zeolites. They are, however, x-ray amorphous.¹⁻⁴ They are formed by the dissolution of a solid aluminosilicate in a solution of alkali hydroxide or alkali silicate to form aluminosilicate ions which subsequently polymerise. The effects of adding magnesium to metakaolin geopolymer systems was examined. Magnesium was added as soluble magnesium salts and as magnesium oxide and hydroxide. When added as a soluble salt, an amorphous magnesium (alumino)silicate with a lower degree of silicate polymerisation than a geopolymer is formed. When added as the oxide or hydroxide, hydrotalcite is formed. In both cases, the product is produced alongside a separate geopolymer phase. A magnesiumcontaining geopolymer phase was not found in either. When heated to 1200°C, geopolymers with magnesium oxide added bloated to form lightweight foams. Lithium analogues of conventional metakaolin geopolymer systems with a range of lithium, aluminium, silicon and water contents were examined. Systems with molar ratios similar to those of commonly studied sodium and potassium metakaolin geopolymers produce self-pelletised lithium zeolites. The zeolite formed was Li-EDI, the lithium analogue of zeolite F. This is the first reported synthesis directly from metakaolin. True lithium geopolymers are found not to form in the systems examined. The zeolite bodies react to form β-eucryptite and β-spodumene at temperatures from 800 – 1350°C. The use of aluminium hydroxide and amorphoud silica rather than aluminosilicates as raw materials for the formation of potassium geopolymers was found to produce geopolymers with embedded grains of unreacted silica and aluminium hydroxide.</p>

Hydrothermal Synthesis and Structural Investigation of a Crystalline Uranyl Borosilicate

The relevance of multidimensional and porous crystalline materials to nuclear waste remediation and storage applications has motivated exploratory research focused on materials discovery of compounds, such as actinide mixed-oxoanion phases, which exhibit rich structural chemistry. The novel phase K1.8Na1.2[(UO2)BSi4O12] has been synthesized using hydrothermal methods, representing the first example of a uranyl borosilicate. The three-dimensional structure crystallizes in the orthorhombic space group Cmce with lattice parameters a = 15.5471(19) Å, b = 14.3403(17) Å, c = 11.7315(15) Å, and V = 2615.5(6) Å3, and is composed of UO6 octahedra linked by [BSi4O12]5− chains to form a [(UO2)BSi4O12]3− framework. The synthesis method, structure, results of Raman, IR, and X-ray absorption spectroscopy, and thermal stability are discussed.

Advances in microbial remediation for heavy metal treatment: a mini review

In recent years, microbiological treatment to remediate contamination by heavy metals has aroused public attention as such pollution has seriously threatens ecosystems and human health and impedes sustainable development. However, the aspect of actual industrial wastewater and solid waste remediation by microorganisms is not explored sufficiently. And what we focus on is technical field of microbial remediation. Therefore, in this review, we discuss and summarize heavy metal treatment via microbiological approaches in different media, including wastewater, solid waste from industrial factories and polluted sites. We also clarify the technical applicability from the perspective of biosorption, bioleaching, biominerization, etc. In particular, the exploration of the combination of microbiological approaches with chemical methods or phytoextraction are scrutinized in this review relative to real waste heavy metal remediation. Furthermore, we highlight the importance of hyperaccumulator endophytes. Graphical abstract