We report the use of solid Lewis
acid catalysts for the conversion
of tetrose sugars to four-carbon α-hydroxy acid esters (C4-AHA), which are useful as functional polyester building blocks.
Sn-β was by far the most active and selective catalyst, yielding
up to 80% methyl vinyl glycolate (MVG), methyl-4-methoxy-2-hydroxybutanoate
(MMHB), and α-hydroxy-γ-butyrolactone (HBL) combined at
95% conversion. A very high turnover frequency (TOF) of 330 molC4‑AHA molSn h–1 was attained
using Sn-β, a more than 6-fold increase compared with homogeneous
SnCl4·5H2O. It is shown that, using different
Sn-based catalysts with various pore sizes, the product distribution
is strongly dependent on the size of the catalyst pores. Catalysts
containing mainly mesopores, such as Sn-MCM-41 or Sn-SBA-15, prefer
the production of the more bulky MMHB, whereas microporous catalysts
such as Sn-β or Sn-MFI favor the production of MVG. This effect
can be further enhanced by increasing the reaction temperature. At
363 K, only 20% MVG is attained using Sn-β, but at 433 K, this
increases to 50%. Using a kinetic analysis, it was found that, in
microporous catalysts, steric hindrance near the Sn active site in
the catalyst pores plays a dominant role in favoring the reaction
pathway toward MVG. Moreover, the selectivity toward both products
is kinetically controlled.
This study reports on the impact of the curing conditions on the mechanical properties and leaching of inorganic polymer (IP) mortars made from a water quenched fayalitic slag. Three similar IP mortars were produced by mixing together slag, aggregate and activating solution, and cured in three different environments for 28 d: a) at 20°C and relative humidity (RH)~50% (T20RH50), b) at 20°C and RH≥90% (T20RH90) and c) at 60°C and RH~20% (T60RH20). Compressive strength (EN 196-1) varied between 19 MPa (T20RH50) and 31 MPa (T20RH90). This was found to be attributed to the cracks formed upon curing. Geochemical modelling and two leaching tests were performed, the EA NEN 7375 tank test, and the BS EN 12457-1 single batch test. Results show that Cu, Ni, Pb, Zn and As leaching occurred even at high pH, which varied between 10 and 11 in the tank test's leachates and between 12 and 12.5 in the single batch's leachates. Leaching values obtained were below the requirements for non-shaped materials of Flemish legislation for As, Cu and Ni in the single batch test.
Abstract:In this work, we explore a novel mineral processing approach using carbon dioxide to promote mineral alterations that lead to improved extractability of nickel from olivine ((Mg,Fe)2SiO4). The precept is that by altering the morphology and the mineralogy of the ore via mineral carbonation, the comminution requirements and the acid consumption during hydrometallurgical processing can be reduced. Furthermore, carbonation pre-treatment can lead to mineral liberation and concentration of metals in physically separable phases. In a first processing step, olivine is fully carbonated at high CO2 partial pressures (35 bar) and optimal temperature (200 °C) with the addition of pH buffering agents. This leads to a powdery product containing high carbonate content. The main products of the carbonation
OPEN ACCESSMetals 2015, 5 1621 reaction include quasi-amorphous colloidal silica, chromium-rich metallic particles, and ferro-magnesite ((Mg1−x,Fex)CO3). Carbonated olivine was subsequently leached using an array of inorganic and organic acids to test their leaching efficiency. Compared to leaching from untreated olivine, the percentage of nickel extracted from carbonated olivine by acid leaching was significantly increased. It is anticipated that the mineral carbonation pre-treatment approach may also be applicable to other ultrabasic and lateritic ores.
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