Charles Q. Jia

The effects of snow and ice on the environmental behaviour of hydrophobic organic chemicals

A review is presented of the roles of snow and ice as they influence the environmental fate of hydrophobic organic chemicals (HOCs). Measurements of HOC concentrations in snow are reviewed and present information on the partitioning and depositional and post-depositional behaviour of HOCs in snow is described and implications for environmental monitoring and assessment of fate are discussed. It is concluded that snow is an efficient scavenger of HOCs from the atmosphere both by adsorption of gaseous HOCs to the ice interface, and by particle scavenging. The post-depositional fate of HOCs in ageing snow packs is poorly understood. Suggested structures of quantitative models describing HOC interactions with ice and snow are presented. Key parameters in these models include the interfacial area of snow and the extent of HOC sorption to the ice surface. Recent laboratory determinations of these parameters are reviewed. Finally, research needs and gaps are identified with a view to compiling more accurate estimates of net atmospheric wet deposition of HOCs, establishing their fate in snow packs, developing reliable sampling protocols and assessing the usefulness of the glacial record as an indicator of past atmospheric compositions.

Adsorption of polycyclic aromatic hydrocarbons from water using petroleum coke-derived porous carbon

Porous carbons were prepared from petroleum coke by KOH chemical activation, characterized and used as adsorbents for uptaking a mixture of polycyclic aromatic hydrocarbons (PAHs): naphthalene, fluorene, phenanthrene, pyrene and fluoranthene from aqueous solutions. The specific surface area (SSA) of these carbons ranges from 562 to 1904 m2/g, while their point of zero charge (pH(PZC)) varies from 2.6 to 8.8. The equilibrium adsorption of PAHs on all four carbons follows the non-linear Freundlich equation well. For any given PAH in the group, the adsorption capacity parameter K(f), increases with the SSA and pH(PZC) of the carbons, confirming the roles of dispersive interactions. For any given carbon, the value of K(f) follows the order of naphthalene > fluorene > phenanthrene > pyrene. This dependence of K(f) on molecular size suggests a certain degree of molecular sieving behavior of these carbons toward large PAHs. Under the condition studied, the uptake process is likely controlled by diffusive transport processes. And, it is unlikely that the competitive adsorption played any important roles in determining equilibrium adsorption of the mixed PAHs. Overall, the petroleum coke-derived porous carbon is very effective in adsorbing these PAHs.

Sorption and stability of mercury on activated carbon for emission control.

A leading strategy for control of mercury emissions from combustion processes involves removal of elemental mercury from the flue gas by injection of activated carbon sorbent. After particulate capture and disposal in a landfill, it is critical that the captured mercury remains permanently sequestered in the sorbent. The environmental stability of sorbed mercury was determined on two commercial, activated carbons, one impregnated using gaseous sulfur, and on two activated carbons that were impregnated with sulfur by reaction with SO(2). After loading with mercury vapor using a static technique, the stability of the sorbed mercury was characterized by two leaching methods. The standard toxicity characteristic leaching procedure showed leachate concentrations well below the limit of 0.2mg/L for all activated carbons. The nature of the sorbed mercury was further characterized by a sequential extraction scheme that was specifically optimized to distinguish clearly among the highly stable phases of mercury. This analysis revealed that there are two forms in which mercury is sequestered. In the sorbent that was impregnated by gaseous sulfur at a relatively low temperature, the mercury is present predominantly as HgS. In the other three sorbents, including two impregnated using SO(2), the mercury is predominantly present in the elemental form, physisorbed and chemisorbed to thiophene groups on the carbon surface. Both forms of binding are sufficiently stable to provide permanent sequestration of mercury in activated carbon sorbents after disposal.

Behaviour of Co and Ni during aqueous sulphur dioxide leaching of nickel smelter slag

Abstract The behaviour of Co and Ni during aqueous sulphur dioxide leaching of nickel smelter slag from INCO was studied. The study is part of a major research project aimed at developing an effective means for extracting valuable metals from slag using aqueous sulphur dioxide. Leaching experiments were carried out under different conditions in a batch reactor. Maximum extractions of Co and Ni after 3 h were 77% and 35%, respectively. The rate of extraction of both metals was independent of stirring speed between 450 and 700 rpm. The shrinking core model was used to explain the behaviour of Co and Ni. Co extraction was limited by both ash layer diffusion and surface chemical reaction, whereas Ni extraction was limited only by ash layer diffusion. Scanning electron microscopy–energy dispersive spectroscopy analysis showed that the slag becomes porous after leaching and follows the shrinking core-form of dissolution.

The behaviour of selected heavy metals in MSW incineration electrostatic precipitator ash during roasting with chlorination agents

Abstract The thermal behaviour from 500–1050°C of selected heavy metals (Pb, Zn, Cu and Cd) in the electrostatic precipitator (ESP) ash from a municipal solid waste (MSW) incinerator was studied on a laboratory scale. The parameters studied included temperature, reaction time, type of chlorination agent, and amount of chlorination agent. The vaporization and removal of these metals are characterized by the formation and volatilization of the metal chlorides, and are dependent on temperature and time. As a result of volatilization, ≈ 90% of Pb, Zn, Cu and Cd can be removed from the ESP ash under the conditions studied. The fraction of metal removed is determined mainly by the relative stabilities of the metal chloride and oxide. The results provide a basis for the development of a thermal treatment process to convert the ESP ash from potentially hazardous into non-hazardous material and to recover the selected metals from the ash.

Characterization of smelter slags

Abstract The chemical and phase compositions of four different slags were studied with emphases on the form of Nickel, Cobalt and Copper. These were INCO slow cooled (IS), INCO fast cooled (IF), Falconbridge‐Sudbury fast cooled (FFS) and Falconbridge‐Timmins fast cooled (FFT) slags. The amount of each of Ni, Co and Cu in all the slags was less than 1%. IS contained the highest amount of Ni and Co of 0.57% and 0.21% respectively. The highest Cu content was found in FFS (0.87 %). The form of Co in all the slags was primarily oxide (> 98%). However, significant portions of Ni and Cu (20%) in IF and IS slag were in the sulphide form. Finer fractions (<270 mesh) of these slags were richer in sulphide forms of Ni and Cu (40%). X‐ray analysis revealed FFS and FFT as predominantly amorphous. Both slags were homogenous, consisting of mainly iron silicate glass. However, IF and IS slags were mostly crystalline, with two predominant phases, fayalite and spinel. In addition, a smaller amount of feldspar (albite) was observed in IS. Reflected light microscopy observation showed more crystalline phases in IS than IF. SEM‐EDS analysis, EMPA elemental mapping and reflected light microscopy studies all indicated the presence of entrained sulphide particles in the slag samples.

The chemistry of aqueous S(IV)-Fe-O2 system: state of the art

The aqueous Fe-S(IV)-O2 system is kinetically superior to pure O2 in oxidizing inorganic (e.g., As(III) to As(V), S(IV) to S(VI)) or organic (e.g., phenol) compounds and can achieve EH levels (>1.3 V) that exceeds the O2-H2O couple. Fe-S(IV)-O2 is important in various geochemical, biochemical, atmospheric, and industrial processes, and thus much effort has been devoted to understanding the mechanistic aspect of its redox chemistry. Despite the many advances made recently, Fe-S(IV)-O2 redox chemistry has not been fully understood and elucidated. Clarification is needed on the redox chemistry of Fe-S(IV)-O2: from a mechanistic level (e.g. mode of catalysis, effects of ligand) to its relative importance in various natural processes (e.g., acid rain formation). We attempt to initiate some of these clarifications by: 1) critically examining experimental results, conclusions, and disagreements found in literature, 2) considering the Fe-S(IV)-O2 system in the light of other relevant chemistries, 3) highlighting difficulties in experimental practice that can interfere with the chemistry of Fe-S(IV)-O2, and 4) discussing future research needs. This review ends with a large compilation of available thermodynamic properties (complex stability constants, ) and kinetic data (rate expression, rate constants) relevant to Fe-S(IV)-O2 system.

Roles of Sulfuric Acid in Elemental Mercury Removal by Activated Carbon and Sulfur-Impregnated Activated Carbon

This work addresses the discrepancy in the literature regarding the effects of sulfuric acid (H(2)SO(4)) on elemental Hg uptake by activated carbon (AC). H(2)SO(4) in AC substantially increased Hg uptake by absorption particularly in the presence of oxygen. Hg uptake increased with acid amount and temperature exceeding 500 mg-Hg/g-AC after 3 days at 200 °C with AC treated with 20% H(2)SO(4). In the absence of other strong oxidizers, oxygen was able to oxidize Hg. Upon oxidation, Hg was more readily soluble in the acid, greatly enhancing its uptake by acid-treated AC. Without O(2), S(VI) in H(2)SO(4) was able to oxidize Hg, thus making it soluble in H(2)SO(4). Consequently, the presence of a bulk H(2)SO(4) phase within AC pores resulted in an orders of magnitude increase in Hg uptake capacity. However, the bulk H(2)SO(4) phase lowered the AC pore volume and could block the access to the active surface sites and potentially hinder Hg uptake kinetics. AC treated with SO(2) at 700 °C exhibited a much faster rate of Hg uptake attributed to sulfur functional groups enhancing adsorption kinetics. SO(2)-treated carbon maintained its fast uptake kinetics even after impregnation by 20% H(2)SO(4).

Sequential Extraction Study of Stability of Adsorbed Mercury in Chemically Modified Activated Carbons

Activated carbons chemically modified with sulfur and bromine are known for their greater effectiveness in capturing vapor Hg from coal combustion and other industrial flue gases. The stability of captured Hg in spent activated carbons determines the final fate of Hg and is critical to devising Hg control strategy. However, it remains a subject that is largely unknown, particularly for Br-treated activated carbons. Using a six-step sequential extraction procedure, this work evaluated the leaching potential of Hg captured with four activated carbons, one lignite-derived activated carbon, and three chemically treated with Br(2), KClO(3), and SO(2). The results demonstrated clearly the positive effect of Br- and SO(2)-treatment on the stability of captured Hg. The Hg captured with brominated activated carbon was very stable and likely in the form of mercurous bromide complex. Sulfur added at high temperature with SO(2) was able to stabilize a majority of Hg by forming sulfide and possibly sulfonate chelate. The presence of sulfate however made a small fraction of captured Hg (<10%) labile under mild conditions. Treating activated carbon with KClO(3) lowered the overall stability of captured Hg. A positive dependence of Hg stability on Hg loading temperature was observed for the first time.

Sulfur speciation in fluid coke and its activation products using K-edge X-ray absorption near edge structure spectroscopy

Fluid coke is a by-product of bitumen upgrading process and a stockpiled industrial waste produced in large quantities in Alberta, Canada (overall 10,000 tonnes per day). It has been used as a raw material for manufacturing sulfur-impregnated activated carbon (SIAC). Properties of sulfur in the SIAC are critical to the effectiveness of SIAC in adsorbing mercury at ppb levels. K-edge X-ray absorption near edge structure (XANES) spectroscopy was employed to characterize sulfur in two fluid coke samples and their activation products. It was found that about 90% of sulfur in two coke samples is of organic nature, with over 50% of sulfur in the form of thiophene and the rest 40% being organic sulfide. About 10% of sulfur is in the form of oxides, i.e. sulfate. To simulate the coke samples and validate the analytical technique, a mixture of pure sulfur compounds and graphite was prepared and examined with XANES; the results showed good agreement between the actual and measured sulfur contents in specific forms. XANES results were found to be consistent with X-ray photoelectron spectroscopy (XPS) results. The two techniques are complementary to each other; XANES is capable of distinguishing sulfur species at low oxidation states whereas XPS is able to separate some sulfur species with higher oxidation state. The activation process with KOH and SO2 affected the chemistry of sulfur in fluid coke. XANES surface analysis identified disulfide, sulfide, sulfonate, and sulfate in SIACs and found no thiophene, suggesting a complete removal of thiophene from carbon surface by KOH.