Lionel J. J. Catalan

Study of the physical and chemical mechanisms influencing the long-term environmental stability of natrojarosite waste treated by stabilization/solidification.

Natrojarosite is a residue of zinc refining generated in large quantities by zinc producers in many parts of the world. Stabilization/solidification (s/s) is currently used to immobilize heavy metals prior to storage of the solidified material as a heap. Our study aimed at assessing the long-term environmental stability of treated natrojarosite waste in the field situation. Flow-through leaching tests were carried out on monolithic samples in a modified triaxial cell and on crushed samples in packed columns. Tests with monolithic samples simulated natural infiltration through treated material containing few cracks and fractures, whereas, packed column tests were more representative of weathered material. The microstructure of leached and unleached materials was characterized by scanning electron microscopy and X-ray energy dispersive spectrometry (SEM-EDX). The results of flow-through leaching tests combined with microscopic characterization and geochemical equilibrium calculations provided valuable insights on the physical and chemical mechanisms influencing the long-term leaching behavior. This information was used to develop a mathematical model for alkalinity depletion in the treated waste. When infiltration of acid rain through the material was considered, the model predicted that the leachate would remain at high pH for many thousands of years in the field.

Effects of carbonation on the leachability and compressive strength of cement-solidified and geopolymer-solidified synthetic metal wastes.

The effects of accelerated carbonation on the compressive strength and leachability of fly ash-based geopolymer and ordinary portland cement (OPC) doped with Cd(II), Cr(III), Cr(VI), Cu(II), Pb(II) or Zn(II) salts were investigated. Cement was effective at immobilizing Cd, Cr(III), Cu, Pb and Zn under both the Synthetic Precipitation Leaching Procedure (SPLP) and the Toxicity Characteristic Leaching Procedure (TCLP), but ineffective for retaining Cr(VI). Carbonated cement maintained its ability to immobilize Cd, Cr(III), Pb and Zn, but, under acidic TCLP conditions, was much worse at retaining Cu. Geopolymer was effective at immobilizing Cr(III) and Cu, and, to a lesser degree, Cd, Pb and Zn in SPLP leaching tests. Only Cr(III) was immobilized under comparatively acidic TCLP testing conditions. Carbonation did not change the metal retention capacity of the geopolymer matrix. Metal doping caused compressive strengths of both geopolymer and cement to decrease. Carbonation increased the compressive strength of cement, but decreased that of the geopolymer. Geochemical equilibrium modeling provided insight on the mechanisms of metal immobilization.

Periodicities in the high-mass X-ray binary system RX J0146.9+6121/LS I+61°235

The high-mass X-ray binary RX J0146.9+6121, with optical counterpart LS I+61 ◦ 235 (V831 Cas), is an intriguing system on the outskirts of the open cluster NGC 663. It contains the slowest Be type X-ray pulsar known with a pulse period of around 1400 s and, primarily from the study of variation in the emission line profile of Hα, it is known to have a Be decretion disc with a one-armed density wave period of approximately 1240 d. Here we present the results of an extensive photometric campaign, supplemented with optical spectroscopy, aimed at measuring short time-scale periodicities. We find three significant periodicities in the photometric data at, in order of statistical significance, 0.34, 0.67 and 0.10 d. We give arguments to support the interpretation that the 0.34 and 0.10 d periods could be due to stellar oscillations of the B-type primary star and that the 0.67 d period is the spin period of the Be star with a spin axis inclination of 23 +10 −8 degrees. We measured a systemic velocity of −37.0 ± 4.3 km s −1 confirming that LS I+61 ◦ 235 has a high probability of membership in the young cluster NGC 663 from which the system’s age can be estimated as 20–25 Myr. From archival RXTE All Sky Monitor (ASM) data we further find ‘super’ X-ray outbursts roughly every 450 d. If these super outbursts are caused by the alignment of the compact star with the one-armed decretion disc enhancement, then the orbital period is approximately 330 d.

Effects of process changes on concentrations of individual malodorous sulphur compounds in ambient air near a Kraft pulp plant in Thunder Bay, Ontario, Canada

Ambient air samples were collected at several locations in the community around a major Canadian pulp and paper plant over a period of several months, before and after major process changes. These changes, which occurred in the spring of 2006, included the closure of one of two Kraft pulp mills on site and the shutting down of a chemical recovery boiler and associated black liquor oxidation systems. The facility currently operates one Kraft mill producing both hardwood and softwood market pulp and a two machine paper mill with thermomechanical and deinking pulp mills. All ambient air samples were collected downwind from the plant in Teflon bags and analyzed for volatile reduced sulphur compounds using a gas chromatograph equipped with a pulsed flame photometric detector and a cryogenic trapping system. The frequency distributions of the concentrations of hydrogen sulphide (H2S), methyl mercaptan (CH3SH), dimethyl sulphide (DMS), and dimethyl disulphide (DMDS) were compared before and after the process changes. DMS was found to be the most abundant reduced sulphur compound in ambient air before the changes with an average concentration of 1.49 ppbv. After the changes, the average concentrations of CH3SH, DMS, and DMDS decreased by 28, 70, and 58%, respectively. The concentration of H2S was below its detection limit of 0.90 ppbv in most of the samples collected both before and after the process changes.

A Comparison of Methods for Determining Carbonation Depth in Fly Ash-blended Cement Mortars

Several methods were compared for measuring depth of carbonation in 50.8 x 101.6 mm (2 x 4 in.) mortar cylinders that had been prepared from ordinary portland cement, with 0 to 40% Type C coal fly ash (FA) substitution, and reacted for up to 28 days in an atmosphere of 50% CO₂ at 62% relative humidity (RH). Freshly split sections were analyzed by traditional phenolphthalein staining, digital image analysis (stained and unstained), pH profiling of aqueous digests, and Fourier-transform infrared spectrophotometry. Advancement of the carbonation front was modeled using the diffusion-limited unreacted core model, illustrating that partial substitution of portland cement by FA increased the rate of sample carbonation. The traditional phenolphthalein method significantly underestimated the advancement of the carbonation fronts leading edge. The other techniques were all in reasonable agreement with one another. However, of these, digital image analysis was the fastest and least expensive method to carry out.

Decommissioning of Copper Heap-Leach Residues by Rinsing with Water and Alkaline Solutions - A Pilot Scale Study

Acid heap leaching is widely applied around the world for the purpose of recovering copper from copper oxide ores. Nevertheless, environmental issues associated with the large volumes of spent ore left by leaching have received only limited attention from the mining and research communities. At sites with a positive water balance, seepage contaminated with residual metals resulting from infiltration of rain and snow melt through the spent heap is expected after the leaching operation ceases. This contamination could require treatment of the seepage for centuries. In this study, sequential rinsing of spent copper oxide ore with fresh water and alkaline solutions was tested for accelerating the removal and the neutralization of contaminants. Four thousand tons of ore contained in a vat were initially leached by applying acid solution onto the ore with drip emitters mounted on irrigation tubes, a common method for solution distribution in full-scale operations. Next, rinsing was carried out first with drip e...