Formation Of Water-soluble Compounds Research Articles

Study on selective green leaching of rare earth elements from coal gangue using mechanochemical activation

This study proposes a sustainable method for the selective leaching of rare earth elements (REEs) from coal gangue. By combining 600 °C calcination, the addition of 5 % Fe2(SO4)3, and one hour of mechanical-chemical activation, we achieved a leaching efficiency of 65 % for REEs. This method alters the surface and crystalline structure of coal gangue, facilitating the release of rare earth phosphate minerals and the formation of water-soluble compounds (rare earth sulfates). Fe2(SO4)3 transforms into insoluble iron oxide, which immobilizes impurities and promotes the selective leaching of rare earth elements. Notably, during the leaching process, the leaching rates of aluminum (Al) and iron (Fe) were only 0.37 % and 1.27 %, respectively. Kinetic analysis indicates that this process follows a mixed reaction-controlled shrinking core model. This method effectively reduces the environmental risks associated with traditional acidic reagents, providing a sustainable pathway for the recovery of rare earth elements.

Comparison between the “one-step” and “two-step” catalytic pyrolysis of pine bark

In this study, one-step and two-step pyrolysis systems were compared in the pyrolysis of pine bark. One-step pyrolysis was performed in a fixed bed reactor with and without catalyst. Two-step pyrolysis was carried out in a dual reactor system over catalyst; the first reactor containing no catalyst whereas the second reactor containing catalyst to upgrade the thermally cracked products. The catalysts used in the pyrolysis systems were ReUS-Y, red mud and ZSM-5. In thermal pyrolysis, the pyrolysis system mainly affected the relative amount of bio-oil. The bio-oil yields obtained from two-step thermal pyrolysis were higher than the yields from one-step thermal pyrolysis. In the catalytic runs, ReUS-Y catalyst slightly decreased the char formation with a consequent increase in aqueous phase yield in the case of one-step pyrolysis. However, the catalysts decreased the bio-oil yield with a consequent increase in the gas yield in the case of two-step pyrolysis. The general compositions of bio-oils obtained from both two pyrolysis systems were affected by using catalysts. In the case of one-step pyrolysis, the formation of water and water soluble compounds were reduced by using ReUS-Y catalyst. In the case of two-step pyrolysis, both ZSM-5 and red mud increased the formation of water soluble compounds while they decreased water formation. In contrast, ReUS-Y decreased the formation of water soluble compounds and increased the amount of pyrolytic lignin compounds in bio-oil. Fuel characteristics of pyrolysis products (gas, bio-oil and char) for both two pyrolysis systems were also investigated comparatively.

Release of Substances from Secondary Materials in Field Conditions

The objective of this investigation was to determine the concentrations in the seepage water from recycled building materials under field conditions and the influence of the passage through the soil on these concentrations. Using suction cups and lysimeter determinations seepage water was collected from locations with recycled materials and tested for the inorganic parameters: pH, conductivity, sulfate, copper, nickel, arsenic, chromium, and vanadium. The sulfates in the seepage water originate, in particular, from gypsum-containing components of the building materials, and to a lesser degree from brick materials. Increased pH values of up to pH 12 and increased conductivity occur to greater degrees in seepage water from concrete-containing materials due to the release of Ca(OH)2. In the building material layer the lower availability of CO2 means that the carbonatization of the leached calcium hydroxide is delayed. As the pH values increase, more copper and nickel is released due to the formation of water-soluble complexes with ammonia. At some locations the seepage water concentrations of copper, arsenic, and chromium increased likewise with increasing pH values due to the amphoteric character of these heavy metals. The formation of water-soluble compounds under reductive conditions within the water-saturated pieces of building materials means that there is an increased release of arsenic and vanadium into the seepage water. During the passage through the soil the carbonization and oxidizing conditions mean that the concentration of most parameters decreased. The most common contamination of the seepage water is through increased sulfate concentrations.

Rod-like iron(III) oxyhydroxide particles in iron(III)-polysaccharide solutions

The interaction of iron(III) with different anionic polyssacharides has been studied by pH-metric, UV-vis, Fourier transform infrared, viscometric, and conductometric methods. The formation of water-soluble compounds containing surprisingly high numbers of iron(III) ions even at physiological pH has been observed. The complex formation involves carboxylate, sulfonate, and probably alcoholic hydroxylate moieties. The metal binding starts in the acidic pH r region with the complex precipitating at 3.5 ≤ pH ≤ 6. The precipitate dissolves at pH > 6. The compositions of the complexes formed at pH 7 were found to be L[Fe(OH) 3] n , where L is the repeating unit of the polymer. The maximum value of n proved to be dependent not only on the coordination ability, but also on the major mass of the ligands. Viscometric and conductometric data suggest that the structure-determining element of these complexes is the polyssacharide rather than an iron oxyhydroxide cluster. Their solution structure can be described as independent rod-like particles comprising an unfolded polysaccharide backbone and polymerized iron(III)-oxyhydroxide particles.

The interaction between volcanic gases and tephra: Fluorine adhering to tephra of the 1970 hekla eruption

The mass distribution and sorting of tephra produced in the plinian phase of the 1970 Hekla eruption was controlled by the particle size distribution, the height of the eruption column, and velocity of transport. Near the volcano the mass distribution of soluble fluorine was controlled by particle size of the deposits, but approaches the mass distribution of the tephra at longer distances. Adsorbed soluble fluorine reaches a maximum at a distance from the volcano determined by the velocity of the transporting medium. SEM studies show the soluble fluorine to be chemically adsorbed on the surface of tephra particles. The adsorption is shown by experiment to occur at temperatures below 600°C in the cooling eruption column. Evaluation of reactions in the eruption column leads to the conclusion that formation of water soluble compounds adhering to tephra is principally controlled by environmental factors and to a lesser degree by the composition of the volcanic gas phase.