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Numerous research papers on biosorption have been published in the past four decades. This paper reviews and compares heavy metal uptake capacities of various biological and non-biological materials. Adsorption mechanisms and processes of heavy metal ions (HMIs) onto biomasses are summarised and discussed, respectively. In general, all types of adsorbents exhibit certain uptake capacities for HMIs, but the capacity values for different types of biomasses and non-biological materials vary significantly. For HMIs, the reported values for bacterial biomasses typically range from 0.06 mmol·g−1 to 2.84 mmol·g−1; for fungi and yeasts, 0.03 mmol·g−1 to 2.44 mmol·g−1; for fresh water algae, 0.02 mmol·g−1 to 3.15 mmol·g−1; for marine algae, 0.23 mmol·g−1 to 3.77 mmol·g−1; for other biological materials/derivatives, 0.01 mmol·g−1 to 1.78 mmol·g−1 and for non-biological materials, 0.003 mmol·g−1 to 2.40 mmol·g−1. Thereinto, a few macroalgal species exhibit much higher adsorption capacities for HMIs relative to other types of adsorbents. Statistical analysis of heavy metal uptake capacities of various biological and non-biological materials indicates that marine algae are most suitable for the development of industrial biosorbents for the remediation of diluted HMIs-bearing effluents. Biosorption mechanisms of HMIs by biomasses include physical adsorption, ion exchange, electrostatic interaction, surface complexation and inorganic microprecipitation. the physicochemical properties of biosorbents and HMIs as well as external adsorption conditions significantly influence the adsorption process of HMIs onto biomasses. It could be concluded from numerous previous studies that pseudo-first-order and pseudo-second-order models are the most commonly utilised to characterise adsorption process. Up to date biosorption of HMIs remains largely in the laboratory stage. Combining microscopic mechanisms with macroscopic models may be one of the future research directions for removal of HMIs by biomasses. [ABSTRACT FROM AUTHOR]

A natural mud shale (MS) from Yichang Area, China was for the first time experimentally examined for its potential application to oily effluents treatment. The mineralogical compositions, surface structures and pore size distribution of the prepared MS particles were characterised using various advanced analytical technologies, respectively. The performance of the MS particles during the model diesel oil wastewater treatment was examined based on the designed adsorption experiments. Isothermal and kinetic features were investigated according to a variety of adsorption models. The results showed that some pores, cavities and fractures were distributed on the surface of MS particles. The efficiency of MS particles for removing diesel oil from the model oily effluent was associated closely with experimental conditions including the mass of MS particles, initial diesel levels, residence time and pH values. Equilibrium adsorption isotherms conformed to Langmuir model, indicating that the adsorption of diesel oil onto MS particles tended to monolayer adsorption. Kinetics of adsorption of diesel oil on MS complied with the pseudo-second-order model. This suggested that the whole oil removal rate was mainly controlled by chemisorption. Results of our study indicates potential utilisation of unmodified MS particles as an abundant and inexpensive adsorbent for low-concentration diesel oil wastewater. [ABSTRACT FROM AUTHOR]

The distribution and abundance of pyrrolic compoundsin sediments and crude oils are most likely influencedby inorganic sedimentary components. In thispaper, thermal simulation experiments on the systempyrrole-hematite-water were carried out at elevated temperaturesand pressures in order to investigate the effectof organic-inorganic interactions on the preservationof pyrrolic compounds. Compositions of the reactionproducts were analyzed with GC-MS and GC-FIDmethods. In the closed system pyrrole-hematite-water, thenitrogen-oxygen exchange obviously occurred at temperaturesabove 350ºC in accordance with the thermochemicalcalculation. Large amounts of furan and ammonia weregenerated after simulation experiments, indicating thatthe conversion of pyrrole into furan was the dominant reaction.Thermochemical exchange effect between organicnitrogen and inorganic oxygen was obviously facilitatedby elevated temperatures and found to be catalyzed byhematite, but inhibited by the increasing volume of water.Thermodynamically water spontaneously reacts with pyrroleabove 300ºC. The reaction of pyrrole-hematite-wateris an exothermic process in which the reaction heat positivelycorrelates with temperature. The heat released wasestimated as 9.0 KJ/(mol) pyrrole - 15.0 KJ/(mol) pyrrole intypical oil reservoirs (100ºC–150ºC) and 15.0–23.0 KJ/(mol)pyrrole in typical gas reservoirs (150ºC–200ºC). The calculatedactivation energy of the nitrogen-oxygen atom exchangeis about 129.59 kJ/mol. According to the experimentalresults, a small amount of water may effectivelyinitiate the nitrogen-oxygen exchange. The study wouldimprove our evaluating of the preservation and fate ofpyrrolic compounds in deeply buried geologic settings andfurther understanding of thermochemical processes behindthe degradation of petroleum.

Sulfate rocks and organic sulfur from sedimentary organic matter are conventionally assumed as the original sulfur sources for hydrogen sulfide (H2S) in oil and gas reservoirs. However, a few recent experiments preliminarily indicate that the association of pyrite and hydrocarbons may also have implications for H2S generation, in which water effects and natural controls on the evolution of pyrite sulfur into OSCs and H2S have not been evaluated. In this study, laboratory experiments were conducted from 200 to 450°C to investigate chemical interactions between pyrite and hydrocarbons under hydrothermal conditions. Based on the experimental results, preliminary mechanism and geochemical implications were tentatively discussed. Results of the experiments showed that decomposition of pyrite produced H2S and thiophenes at as low as 330°C in the presence of water and n-pentane. High concentrations of H2S were generated above 450°C under closed pyrolysis conditions no matter whether there is water in the designed experiments. However, much more organic sulfur compounds (OSCs) were formed in the hydrous pyrolysis than in anhydrous pyrolysis. Generally, most of sulfur liberated from pyrite at elevated temperatures was converted to H2S. Water was beneficial to breakdown of pyrite and to decomposition of alkanes into olefins but not essential to formation of large amounts of H2S, given the main hydrogen source derived from hydrocarbons. In addition, cracking of pyrite in the presence of 1-octene under hydrous conditions was found to proceed at 200°C, producing thiols and alkyl sulfides. Unsaturated hydrocarbons would be more reactive intermediates involved in the breakdown of pyrite than alkanes. The geochemistry of OSCs is actually controlled by various geochemical factors such as thermal maturity and the carbon chain length of the alkanes. This study indicates that the scale of H2S gas generated in deep buried carbonate reservoirs via interactions between pyrite and natural gas should be much smaller than that of thermochemical sulfate reduction (TSR) due to the scarcity of pyrite in carbonate reservoirs and the limited amount of long-chained hydrocarbons in natural gas. Nevertheless, in some cases, OSCs and/or low contents of H2S found in deep buried reservoirs may be associated with the deposited pyrite-bearing rock and organic matters (hydrocarbons), which still needs further investigation. [ABSTRACT FROM AUTHOR]

In this study, thermal reduction of MgSO by NHCl was operated in the presence of water at 350 °C for 168 h. It was found that NHCl reacted with MgSO to produce HS, N and MgCl as the main products. Based on the experimental results and the assumption that the MgSO-NHCl reaction could approach a state of chemical equilibrium in natural environments over geological time scales, thermochemical program HSC 6.0 was utilized to model this geochemical process occurring in sedimentary basins. The results indicate that NH thermodynamically more easily participates in the reduction of SO than C-C normal alkanes of oil and gas at reservoir temperatures. The heat liberated from the reaction of MgSO-NHCl was estimated as 200.40-270.50 J/mol MgSO in typical oil and gas reservoirs (100-200 °C), which is much smaller than previous studies. In comparison with the minimum temperature range (100-140 °C) for conventional thermochemical sulfate reduction (TSR) using hydrocarbons, the inferred threshold temperature for initiating reduction of SOby NH in geological settings is only about 50-60 °C. The present study shows NH may play an additional role in TSR process by serving as an inorganic reductant, which has substantial implications for the formation of HS and N in sedimentary basins. [ABSTRACT FROM AUTHOR]

H2-rich gas in carbonate reservoirs is usually attributed to thermochemical sulfate reduction (TSR). In this paper, thermal simulation experiments on the reaction system of CH4-MgSO4-H2O were carried out using autoclave at 425°C-525°C. The threshold temperature for initiating TSR is much lower than our previous studies (550°C). Properties of the reaction products were analyzed by microcoulometry, gas-chromatography (GC), Fourier transform-infrared spectrometry (FT-IR) and X-ray diffraction (XRD) methods. Thermodynamics and reaction kinetics of TSR processes were investigated on the basis of the experimental data. The results show that thermochemical reduction of magnesium sulfate with methane can proceed spontaneously to produce magnesium oxide, hydrogen sulfur, and carbon dioxide as the main products, and high temperature is thermodynamically favorable to the reaction. According to the reaction model, the calculated activation energy of TSR is 101.894 kJ/mol, which is lower than that by most previous studies. Mg2+ may have played a role of catalytic action in the process of TSR. The elementary steps of TSR and reaction mechanism were discussed tentatively. The study can provide important information on the explanation of geochemical depth limit for natural gas and on the generation of high H2S gas in deep carbonates reservoirs. [ABSTRACT FROM AUTHOR]