Tuneable separation of gold by selective precipitation using a simple and recyclable diamide

The efficient separation of metals from ores and secondary sources such as electronic waste is necessary to realising circularity in metal supply. Precipitation processes are increasingly popular and are reliant on designing and understanding chemical recognition to achieve selectivity. Here we show that a simple tertiary diamide precipitates gold selectively from aqueous acidic solutions, including from aqua regia solutions of electronic waste. The X-ray crystal structure of the precipitate displays an infinite chain of diamide cations interleaved with tetrachloridoaurate. Gold is released from the precipitate on contact with water, enabling ligand recycling. The diamide is highly selective, with its addition to 29 metals in 2 M HCl resulting in 70% gold uptake and minimal removal of other metals. At 6 M HCl, complete collection of gold, iron, tin, and platinum occurs, demonstrating that adaptable selective metal precipitation is controlled by just one variable. This discovery could be exploited in metal refining and recycling processes due to its tuneable selectivity under different leaching conditions, the avoidance of organic solvents inherent to biphasic extraction, and the straightforward recycling of the precipitant.

Mixotrophic Iron-Oxidizing Thiomonas Isolates from an Acid Mine Drainage-Affected Creek

ABSTRACT Natural attenuation of heavy metals occurs via coupled microbial iron cycling and metal precipitation in creeks impacted by acid mine drainage (AMD). Here, we describe the isolation, characterization, and genomic sequencing of two iron-oxidizing bacteria (FeOB) species: Thiomonas ferrovorans FB-6 and Thiomonas metallidurans FB-Cd, isolated from slightly acidic (pH 6.3), Fe-rich, AMD-impacted creek sediments. These strains precipitated amorphous iron oxides, lepidocrocite, goethite, and magnetite or maghemite and grew at a pH optimum of 5.5. While Thiomonas spp. are known as mixotrophic sulfur oxidizers and As oxidizers, the FB strains oxidized Fe, which suggests they can efficiently remove Fe and other metals via coprecipitation. Previous evidence for Thiomonas sp. Fe oxidation is largely ambiguous, possibly because of difficulty demonstrating Fe oxidation in heterotrophic/mixotrophic organisms. Therefore, we also conducted a genomic analysis to identify genetic mechanisms of Fe oxidation, other metal transformations, and additional adaptations, comparing the two FB strain genomes with 12 other Thiomonas genomes. The FB strains fall within a relatively novel group of Thiomonas strains that includes another strain (b6) with solid evidence of Fe oxidation. Most Thiomonas isolates, including the FB strains, have the putative iron oxidation gene cyc2, but only the two FB strains possess the putative Fe oxidase genes mtoAB. The two FB strain genomes contain the highest numbers of strain-specific gene clusters, greatly increasing the known Thiomonas genetic potential. Our results revealed that the FB strains are two distinct novel species of Thiomonas with the genetic potential for bioremediation of AMD via iron oxidation. IMPORTANCE As AMD moves through the environment, it impacts aquatic ecosystems, but at the same time, these ecosystems can naturally attenuate contaminated waters via acid neutralization and catalyzing metal precipitation. This is the case in the former Ronneburg uranium-mining district, where AMD impacts creek sediments. We isolated and characterized two iron-oxidizing Thiomonas species that are mildly acidophilic to neutrophilic and that have two genetic pathways for iron oxidation. These Thiomonas species are well positioned to naturally attenuate AMD as it discharges across the landscape.

PRESIPITASI LOGAM BERAT LIMBAH CAIR LABORATORIUM MENGGUNAKAN NATRIUM SULFIDA DARI BELERANG ALAM

Precipitation of Laboratory Wastewater Heavy Metals by Natural Sulphur Sodium Sulfide Sodium sulfide (Na2S) from natural sulfur has been used for heavy metal precipitation from laboratory wastewater. Heavy metals in laboratory wastewater include mercury (Hg), lead (Pb), chromium (Cr) and zinc (Zn). Initial laboratory wastewater testing was performed by measuring the initial pH and the concentration of heavy metals in the wastewater prior to precipitation using the atomic absorption spectrophotometer. Sulphide precipitation phase consists of variations in the concentration of NaOH, time, temperature, and volume of dissolving Na2S. Parameters for the efficiency of Hg, Pb, Zn and Cr heavy metal precipitation were the initial pH, concentration and rate of stirring of the solution. Results showed that the optimum precipitation efficiency for Zn is achieved by using 10 % Na2S solution with an efficiency of 97.93 %. The most significant reduction in Cr and Hg was the use of 20 % Na2S solution with a precipitation efficiency of 99.24 % and 99.76 % respectively. The optimal efficiency for Pb with a 30 % Na2S solution was 99.68 %. Natural sulfur can reduce the levels of heavy metals in laboratory wastewater by precipitation.Key words: Natural sulfur, Heavy metals, Precipitation, Sodium sulfide, ABSTRAKPresipitasi logam berat dari limbah cair laboratorium telah dilakukan dengan menggunakan natrium sulfida (Na2S) dari belerang alam. Logam berat yang terkandung dalam limbah cair laboratorium diantaranya adalah merkuri (Hg), timbal (Pb), kromium (Cr) dan seng (Zn). Pengujian awal limbah laboratorium dilakukan dengan mengukur pH awal dan kadar logam berat yang terdapat dalam limbah sebelum presipitasi menggunakan pH meter dan spektrofotometer serapan atom. Tahapan presipitasi limbah oleh sulfida meliputi pembuatan variasi konsentrasi NaOH, waktu, suhu, dan volume pelarutan Na2S. Parameter efisiensi presipitasi logam Hg, Pb, Zn, dan Cr meliputi pH, Konsentrasi dan Kecepatan pengadukan. Hasil penelitian menunjukkan efisiensi pengendapan optimal untuk logam Zn terdapat pada penggunaan larutan Na2S 10% dengan efisiensi 97,93%. Larutan Na2S 20% paling banyak menurunkan logam Cr dan Hg dengan efisiensi masing-masing sebesar 99,24% dan99,76%. Efisiensi optimal untuk logam Pb berada pada penggunaan larutan Na2S 30% dengan efisiensi 99,68%. Belerang alam mampu menurunkan kadar logam berat dalam limbah cair laboratorium dengan metode presipitasi.Kata kunci: Belerang alam, Logam berat, Presipitasi, Natrium sulfida

SIMULATION OF METAL TRANSFER BETWEEN CYLINDRICAL ELECTRODES AT ELECTROSPARK ALLOYING

The work is dedicated to the simulation of the processes of erosion and electrode metal transfer at coating formation by an electrospark alloying method. Anode is a cylindrical rod, and cathode – a disk. During discharge pulses the erosion takes place both in anode material, and in cathode material. The anode moves in a spiral along a cathode surface. There are calculated the coefficients of precipitation equal to the probability of metal emitted from the surface of one electrode and falling onto the surface of the opposite electrode. They are constant close to the central cathode axis, but at the anode approach to the cathode end a coefficient of anode metal precipitation on a cathode decreases, a coefficient of cathode metal precipitation on an anode increases. The rates of anode erosion and cathode weight increase when the mass ratio of eroded substance of anode and cathode increases in the course of one discharge. When this ratio is equal to 5, a coefficient of mass transfer achieves 0.8-0.9 it tells of small substance loss during its transfer between electrodes. The model developed is useful for the parameter estimate of mass transfer between cylindrical electrodes at electrospark processing taking into ac-count their dimensions and paths of anode motion.