Arsenic in Chemical and Metallurgical Conversions of Copper-zinc Concentrates

Due to the deterioration of the quality of obtained sulfide-copper concentrates, arsenic circulates and accumulates in the intermediate products, which reduces the quality of the metal and associated product – sulfuric acid. A method of estimation the distribution of impurity elements can be created using the recycling of sulfide concentrates by various technologies (including autogenous smelting, matte conversion and flotation of slags). This technique is based on solving balance equations for iron, copper and arsenic with known compositions of the resulting products. The obtained data were used to assess of the extraction of arsenic into produce outputs (slag, matte, dust, etc.). In this study, the concentration of arsenic in the dust of metallurgical processes and sludge for cleaning acid solutions is confirmed. The increased temperature in the electrostatic precipitator of gas purification of autogenous processes lead to a partial transition of arsenic into the gas stream directed to the sulfuric acid production. It is possible to regulate the fraction of transition of arsenic to dust and sulfuric acid while changing the operating temperature in the electrostatic precipitator. To a lesser extent arsenic is concentrated in the tails of flotation of slag (11.7%) and metallic copper (2.9%). These data are useful for substantiating measures for the wastes recycling and improvement of the ecological environment in the enterprise operating districts. Keywords: arsenic, autogenous melting, matte conversion, slag flotation, purified gas treatment, distribution, dust, sludge

Concentrated sulfuric acid production from non-condensable gases and its effect on alkali and sulfur balances in pulp mills

The pulp and paper industry often encounters challenges that require process improvements to remain competitive. These challenges may include the requirement to meet more stringent environmental regulations, stricter energy policies, or the need to improve product quality, increase production capacity and profitability. As a result, the pulp mills of today have to focus on becoming more efficient by possessing an effective chemical recovery system and reducing chemical losses. The high degree of closure is beneficial for environment, water consumption and mill economy but can upset the Na/S balance and increase the build-up of non-process elements in the system. Installing an acid plant to convert the sulfur containing Non Condensable Gases (NCG) into sulfuric acid will eliminate the NCG as a sulfur input to the recovery cycle, eliminate purchases of sulfuric acid, reduce caustic purchases, and produce additional steam that will positively impact the mill’s heat balance. This paper provides an overview of the OptimumAcid™ technology required to produce sulfuric acid in a pulp mill from NCG, presents some of the unique challenges related to feed variability, and discusses some of the technical features of NORAM’s sulfuric acid OptimumAcid™ process technology and equipment.

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.

Application of Acidophilic Microorganism in the Metal Enrichment of Electroplating Sludge Use the Membrane Bioreactor

Background: Bioleaching is an important technology for treating electroplating sludge. Previous researches have focus on improving the leaching rate of metals in electroplating sludge by bioleaching. However, the concentration of heavy metals in the leachate after single leaching was lower, which is quite unfavorable for subsequent metal recovery. Additionally, membrane bioreactors (MBRs) have been widely used in the field of sewage treatment. Research on the application of bioleaching technology combined with MBRs to enrich metals in electroplating sludge has not been reported. Therefore, in this study, we first combined bioleaching technology and MBRs for metal enrichment in electroplating sludge to obtain the key technology of "acid production - electroplating sludge leaching - leachate regeneration -repeated electroplating sludge leaching - achievement of valuable metal enrichment".Results: In this research, through scaling up from the laboratory scale (shake flasks) to a factory-scale application (10 m³ membrane bioreactors), we mastered the key technology of acid production by acidophilic microorganism, and the acid solution can be repeatedly used for metal leaching. The results showed that the MBR maintained high-density cell growth (≈2.1×109/mL) and a stable sulfuric acid production rate (850 L/h) throughout the entire operational period. Under the above conditions, the maximum cycle number (10 times) for enrichment of the target metals in the electroplating sludge was obtained. Additionally, after the end of the cycle enrichment process, the concentrations of the target metals Ni+, Cu2+, and Zn2+ were 13.867 g/L, 18.118 g/L and 21.075 g/L, respectively, which were highly enriched.Conclusions: This study first solved the difficulties in the industrialization of bioleaching electroplating sludge through combining bioleaching technology and MBRs. Furthermore, this research can provide a demonstration project for the industrial application of MBR-bioleaching technology in electroplating sludge, with a view to applying this technology to the disposal of more types of hazardous waste.

Research progress of low-temperature heat recovery technology in sulfuric acid production

Low-temperature waste heat refers to the sum of the heat degraded and transferred to the dry absorption process after the high- and medium-temperature heat is recovered in the conversion process in the conventional sulfuric acid production plant, as well as the sulfuric acid formation heat, steam condensation heat and sulfuric acid dilution heat generated in the dry absorption process. It is of great practical significance to rationally develop and utilize the low-temperature waste heat. This paper introduces the development of traditional waste heat recovery technology and low-temperature heat recovery technology for sulfur-based sulfuric acid production. It also expounds the principle, process technology and main equipment of developing low-temperature heat recovery technology for sulfuric acid production plants at home and abroad, and summarizes the low-temperature heat recovery technology for sulfuric acid production plants.