Spent sulfuric acid plant catalyst: valuable resource of vanadium or risky residue? Process comparison for environmental implications.

The enormous amount of spent catalysts generated worldwide may pose a risk to the environment because of their high load of metals, including vanadium. The latter may be mobilized and released to the environment if managed improperly. Moreover, the catalysts could be considered as secondary resources rather than waste. This study aimed at the efficient extraction of vanadium from spent desulfurization catalyst (SDC) from a sulfuric acid production plant. The raw SDC and the post-extraction residues were characterized in terms of their chemical and phase composition. The metal mobility from the materials was examined with both single-step and multi-step extractions. The environmental risk assessment was performed using sequential extraction. The study revealed that both tested methods (citric acid leaching and bioleaching with Acidithiobacillus thiooxidans) enable the extraction of nearly 96% of V from SDC with a simultaneous reduction of metal mobility. However, the bacterial treatment was found more suitable. The leached residue was mostly (> 90%) composed of SiO2, which makes it a potential candidate for application in construction (e.g., concrete mixtures) after additional examinations. The study highlights the need to develop a metal extraction process for SDC in a way that metal-free residue could be a final product.

Bacterial leaching of critical metal values from Polish copper metallurgical slags using Acidithiobacillus thiooxidans.

Global economy faces an increasing problem of the supply risk of critical raw materials, therefore the search for secondary resources has become an urgent issue. Copper orebodies in Poland contain substantial amounts of metals deemed critical (e.g. Co, Mo, rare earth elements (REE) or V), which are not recovered during processing. The metals of interest are concentrated in metallurgical waste residues that should be classified as a secondary resource rather than as a waste. Bioleaching is a frontier technology promising for environment-friendly treatment of slags. Therefore, the objective of this work was to study the feasibility of metal (Co, Mo, REE, V) bioleaching from copper metallurgical wastes employing Acidithiobacillus thiooxidans bacterial strain as the leaching agent. The effect of particle size (fractions <0.25 mm and 0.25-0.5 mm) and pulp density (1%, 2%) was studied using three different slag samples (lead slag - LS, shaft furnace slag - SFS and granulated slag - GS). The bioleaching experiment was set up for 28 days under acidic conditions (pH t0 = 2.5). The results revealed that the microorganisms can catalyze metal extraction from slags as compared to leaching achieved under abiotic conditions. The optimal bioleaching yield was achieved under conditions at 0.25-0.5 mm particle size and 1% pulp density, regardless of used type of slag. After 28 days, the extracted amounts of metals were: 88% Co, 40% Mo, 83% REE and 55% V from LS, 100% Co, 44% Mo, 70% REE and 70% V from SFS and 95% Co, 70% Mo, 99% REE and 93% V from GS. All examined slags showed good potential for bioleaching of valuable elements. However, optimization of initial parameters is still needed for further efficiency improvement, especially in terms of the process duration.

Air pollution control and flue gas desulfurization residues from Polish copper smelting facility as adsorbents of Pb(II) and Cu(II) from aqueous solutions.

This study aimed at evaluation of air pollution control residues (APCR) and flue gas desulfurization residues (FGDR) from copper foundry in Southwestern Poland as adsorbents of Cu(II) and Pb(II) from simulated wastewater. Studies of the impact of pH and adsorbent dose, as well as sorption isotherms, and kinetic and thermodynamic studies were conducted in a series of batch experiments. The maximum adsorption capacities were equal to 42.9 mg g-1 Cu(II) and 124.4 mg g-1 Pb(II) for APCR and 98.8 mg g-1 Cu(II) and 124.7 mg g-1 Pb(II) for FGDR, which was comparable to mineral adsorbents examined in other studies. Adsorption isotherms followed the Langmuir model, except for Pb(II) for FGDR, which followed Freundlich model. Sorption kinetics for both materials was properly expressed by pseudo-second-order equation. Mean adsorption energy parameter suggested that the adsorption might have occurred via physical bonding. Thermodynamic study revealed that adsorption was spontaneous and endothermic for Cu(II) and not spontaneous and exothermic for Pb(II), with lower temperature favoring the process. The results suggested that both materials had high affinity towards Cu(II) and Pb(II) ions and could be conducted industrial scale research for consideration as potential adsorbents from aqueous solutions.