Application of Liquidus Projections in SiO2-Al2O3-CaO Systems with Fe2O3 and V2O5 to Study the Dissolution of Alumina Crucibles in Gasification Slags Containing Vanadium.

Entrained flow gasification occurring above 1400 °C is a technique to convert petroleum coke, a byproduct of petroleum refining, into synthesis gas. The molten ash/slag formed in the process has a high amount of V and Ni compounds, which are corrosive to the reactor walls. Slag viscosity is an important parameter that must be controlled to tap the slag from the gasifier. The viscosity of the slags is measured in high-temperature viscometers. Alumina crucibles, used in viscosity measurements, were severely corroded by high V/Ni slags in several in-house experiments. To study the chemistry of these dissolutions, saturation solubilities of alumina crucibles in the slags (at 1500 °C) and precipitated primary phases were determined from liquidus projections prepared in Factsage. The 10 slags considered in this study were composed of SiO2 (<50.2 wt %), Al2O3 (<29.2 wt %), Fe2O3 (<41.4 wt %), CaO (<16.6 wt %), NiO (<20.4 wt %), and V2O5 (<20.5 wt %). The precipitated primary phases were corundum (solid solution), spinel (solid solution), V_spinel (solid solution), mullite (solid solution), and anorthite. Experiments were performed with ash placed on alumina discs in a reducing atmosphere. The ash compositions were based on previous in-house viscosity and ash melting experiments. Saturation solubilities were above 30 wt % in multiple tests with perforated and intact crucibles. In two such cases, hercynite, which can inhibit slag penetration into a crucible, was predicted as a primary phase. In another test with an intact crucible, anorthite, which leads to indirect dissolution, was predicted as a primary phase and was also identified in the X-ray diffraction (XRD) results of the slag-crucible interface. Here, saturation solubility was 8.9 wt %. It was concluded that determination of saturation solubilities and primary phases would lead to successfully measuring the viscosity of slags containing V and Ni in alumina crucibles.

Effect of various ligands on the selective precipitation of critical and rare earth elements from acid mine drainage.

Acid mine drainage (AMD) has been of environmental concern for decades but recently found to be a viable source of critical elements including rare earth elements (REEs). Recovery of these elements while treating AMD for environmental compliance improves the sustainability of the treatment process. The precipitation behavior of the REEs and other cations during the AMD neutralization process depends strongly on the solution chemistry, available ligands, and concentration of elements. Several chemicals were used to study the effect of various ions/ligands (i.e., OH-, SO42-, NH4+, CO32-, and PO43-) on precipitation behavior of REEs and other elements from AMD as a function of pH. It was found that only up to 70% of total REEs can be recovered using NaOH at circumneutral pH. (NH4)OH suppressed the precipitation of REEs up to pH 8. The presence of phosphate and carbonate ions in the solution increased the precipitation yield of REEs at lower pH values. Both Na2HPO4 and Na2CO3 were found to increase the precipitation of REEs at pH below 7, as over 85% of REEs were recovered. Calculated saturation indices and speciation diagrams for selected REEs confirmed the experimental data. Considering the elemental recovery values, environmental effects, as well as chemical consumption and cost, a two-step AMD treatment process using Na2CO3 was formulated. Through the proposed process, 90% of the aluminum was recovered in the first step (at pH 5), while 85% of REEs was recovered in the second step (at pH 7) with a significantly high concentration of 1.6%.

Influence of calcium content of biomass-based materials on simultaneous NOx and SO2 reduction.

Pyrolysis products of biomass (bio-oils) have been shown to cause a reduction in NOx emissions when used as reburn fuels in combustion systems. When these bio-oils are processed with lime, calcium is ion-exchanged and the product is called BioLime. BioLime, when introduced into a combustion chamber, pyrolyzes and produces volatile products that reduce NOx emissions through reburn mechanisms. Simultaneously, calcium reacts with SO2 to form calcium sulfate and thus reduces SO2 emissions. This paper reports the characterization of composition and pyrolysis behavior of two BioLime products and the influence of feedstock on pyrolysis products. Thermogravimetric analysis (TGA) and 13C-CP/MAS NMR techniques were used to study the composition of two biomass-based materials. The composition of the pyrolysis products of BioLime was determined in a laboratory scale flow reactor. The effect of BioLime composition on NOx and SO2 reduction performance was evaluated in a 146.5 kW pilot-scale, down fired combustor (DFC). The effect of pyrolysis gas composition on NOx reduction is discussed. The TGAweight loss curves of BioLime samples in an inert atmosphere showed two distinct peaks corresponding to the decomposition of light and heavy components of the BioLime and a third distinct peak corresponding to secondary thermal decomposition of char. The study also showed that BioLime sample with lower content of residual lignin derivatives and lower calcium content produced more volatile compounds upon pyrolysis inthe combustor and achieved higher NOx reduction (15%). Higher yields of pyrolysis gases increased the NO reduction potential of BioLime through homogeneous gas phase reactions. Calcium in BioLime samples effectively reduced SO2 emissions (60-85%). However, addition of higher calcium content to the BioLime samples also appeared to inhibit the volatile yield and thereby lowered the NOx reduction.