Thermodynamic analysis and application for extracting valuable components from iron-phosphorus residue of spent catalysts.

The method of extracting valuable metals from spent catalysts has been developed in recent years. In this paper, the solid waste produced in the treatment of spent catalyst was studied and named iron-phosphorus residue (IPR). IPR was composed of FePO4·2H2O, Fe3(PO4)2·3H2O, Fe5(PO4)4(OH)3·2H2O, and SiO2. Appreciable quantities of Ni, Co, V, Mo, and W were detected in IPR. Based on E-pH diagrams, different atmospheric leaching strategies were used to extract valuable components from IPR. Both the HCl and NaOH leaching are appropriate for treating IPR. An in-depth investigation on HCl atmospheric leaching showed that >95% of Fe, Ni, Co, V, and Mo, 76.9% of W, and 89.3% of P were extracted efficiently and SiO2 was enriched into the leach residue, at leaching temperature of 90 ℃, leaching time of 180 min, initial HCl concentration of 5 mol/L and liquid to solid ratio of 8:1 mL/g. The leaching mechanism was discussed via XRD, XPS, and FTIR. An efficient and green process for the recovery of valuable components in IPR has been developed. This research achieves the sufficient extraction of valuable components in IPR and provides significant guidance for the management of similar solid waste.

Thermodynamics analysis and response surface methodology to investigate decomposition behaviors for lepidolite sulfation products in presence of coal.

The process consisting of sulfation and decomposition has been proved to utilize lepidolite efficiently, while the conditions of sulfation products are relatively harsh. In this paper, the decomposition behaviors for lepidolite sulfation products in presence of coal were studied to optimize the conditions required. The feasibility was first verified theoretically by calculating the thermodynamic equilibrium composition with different amounts of carbon addition. The priority of each component reacted with carbon was concluded as Al2(SO4)3, KAl(SO4)2, RbAl(SO4)2, and FeSO4. Based on the batch experimental results, response surface methodology was purposed to simulate and predict the effect of various parameters. The verification experimental results showed the extraction of Al and Fe were only 0.05 % and 0.01 % under the optimal conditions of 750 °C, 20 min, and 20 % coal dosage. The separation of alkali metals and impurities was realized. The decomposition behaviors for lepidolite sulfation products in presence of coal was clarified by discussing the contradiction between theoretical thermodynamic calculation and actual experimental results. It indicated that carbon monoxide was more active than carbon in promoting decomposition. The addition of coal decreased the temperature and time required, which not only cut the energy consumption, but also reduced the operation difficulty. This study provided more theoretical and technical support for the application of sulfation and decomposition process.

One-step recovery of cobalt from ammonia-ammonium carbonate system via pressurized ammonia distillation.

Ammonia leaching of Co-bearing resources has attracted attention due to its selectivity to cobalt and mild leaching conditions. However, in ammonia leach liquor, cobalt and ammonia are complexed stably, which undoubtedly increases the difficulty of preparing cobalt products from the solution. In this study, ammonia distillation process was proposed and studied to recover cobalt from NH3-(NH4)2CO3 system. First, the E-pH diagram of Co-NH3-CO32--H2O system was drawn, and the possibility of preparing cobalt products from the solution was discussed. Then, by comparing atmospheric and pressurized ammonia distillation processes, it was found that the microspherical Co3O4 product can be obtained directly through pressurized ammonia distillation. Furtherly, the effects of parameters on this process and the formation mechanism of Co3O4 were investigated systematically. Over 99% of cobalt could be recovered in one step under optimal conditions. Finally, CoCO3 products with different morphologies were also obtained directly by adding the reducing agent during pressurized ammonia distillation, and the cobalt recovery rate was hardly affected. The evaporated ammonia and residual solution can be recycled. This work realizes the one-step preparation of cobalt products and provides a new perspective on cobalt recovery from ammoniacal solution.

A shortcut approach for cooperative disposal of flue dust and waste acid from copper smelting: Decontamination of arsenic-bearing waste and recovery of metals.

Recovering harmful elements (As, Pb) and metals (Cu, Bi, Zn) from copper smelting flue dust (CSFD) is a critical subject and task for arsenic contamination control and resource sustainability. In this work, a two-step pyrometallurgical process was developed to preferentially separate arsenic and recover metals from CSFD. During the low-temperature roasting, arsenic-bearing waste acid (AWA) from copper industry was used as an additive and effective removal of arsenic (97.8 %) was obtained at 350 °C, which follows the idea of "treating waste with waste". Subsequently, the recovery and separation of metals were well-achieved based on the affinity between metals and sulfur in the second stage of roasting, by which 91.28 % of Pb and 95.65 % of Bi were recovered as an alloy (Pb 86.48 %, Bi 13.21 %), while 82.62 % of Cu was enriched in the matte. The migration rules of metal elements and phase transformation in the whole process were studied in-depth from theory and experiments. This process can realize the efficient removal of arsenic as well as effective recovery of metals via cooperative disposal of CSFD and AWA, and minimize the environmental impacts.

Recovering metals from flue dust produced in secondary copper smelting through a novel process combining low temperature roasting, water leaching and mechanochemical reduction.

Flue dust from secondary copper smelting (FDSC) is a hazardous waste as well as a secondary resource due to the high content of Cl, Br, and valuable metals (Pb, Cu, Zn, Cd). Herein, a novel process, combined low-temperature roasting, water leaching, and mechanochemical reduction, was developed for recovering metals from the FDSC. The phase conversion and behavior of the main elements in the whole process were explored based on thermodynamic analysis, experimental research, and various characterization. First, thermodynamics calculation revealed that adding H2SO4 could significantly decrease the roasting temperature and promote the generation of soluble metal sulfates. The experimental results showed that more than 99% of Cl and Br were removed by roasting at 325 °C and 1.5 times H2SO4 addition. Subsequently, the Cu, Zn, and Cd were almost completely leached by water under the conditions of 80 â„ƒ, 2 h and L/S = 5 mL·g-1, while Pb was rejected and enriched in the residue. Finally, using iron powder as a reductant, 96.7% of PbSO4 was reduced to elemental lead at room temperature with the aid of mechanical force. The findings illustrated that the recovery performance of metals and environmental benefits will be greatly improved by the proposed process.

Insights into the effect of cations on cathodic behavior and microstructure in cadmium electrochemical recovery process.

Secondary resources provide an essential source for cadmium recovery, but also bring severe environmental problems. Due to the short process and high product purity, electrodeposition is suitable for realizing the reduction, reuse, and recycling of cadmium, while the complex composition of the resources contributes to a complicated electrochemical system. In this work, the effect of common cations (Cu2+, Ni2+, Fe2+, and Zn2+) on cadmium electrochemical recovery was investigated from the perspective of electrochemical behavior and microstructure. The results indicated that Cu affected the electrochemical process most prominently, which was deposited on the cathode and formed microcell with Cd, not only impeding the recovery of Cd, but also influencing the purity severely. Comparatively, Ni showed a relatively minor effect, which made the formal potential more negative and alleviated cathodic polarization to some degree. Besides, Fe2+ was oxidized by the oxygen released from the anode, and followed by the reaction with Cd, resulting in the redissolution of Cd. With respect to Zn, a low concentration of Zn (≤1 g L-1) had little influence on electrochemical behavior of Cd, while it was deposited simultaneously with Cd on the cathode at a high concentration (5 g L-1). Based on the microstructural characterization, the lithops-like cathode cadmium grew up in the presence of Cu, while dendritic Cd was formed affected by Zn, Fe2+, and Ni, especially Fe2+.

Co-treatment of copper smelting flue dust and arsenic sulfide residue by a pyrometallurgical approach for simultaneous removal and recovery of arsenic.

As the typical hazardous arsenic pollutants, copper smelting flue dust (CSFD) and arsenic sulfide residue (ASR) are produced extensively during copper smelting process, which pose significant pressure on environmental protection and green development of the copper industry. This work proposed an economic, efficient, and applicable approach to treat waste with waste, in which the simultaneous removal and recovery of As from CSFD and ASR were realized by a roasting process, with adding sulfuric acid, at a relatively low temperature (300-350 â„ƒ). The thermodynamic analysis and experiments confirmed that the main phases of As2S3 and S0 in the ASR were used as a reductant for reducing As(Ⅴ) in the CSFD, and the introduction of sulfuric acid favorably enhanced the thermodynamic driving force and greatly lowered the reaction temperature. The results indicated that removal and behavior of As were highly dependent on the mass ratio of ASR to CSFD, roasting temperature, and H2SO4 dosage. By regulating the parameters, the species As2S3, As2O5, and arsenate were all converted to volatile As2O3, which could be captured and deposited in cold water. In the optimized co-treatment, a satisfied As removal efficiency of 96.12% was achieved, while getting the 97.03% pure As2O3.

Efficient removal and recovery of arsenic from copper smelting flue dust by a roasting method: Process optimization, phase transformation and mechanism investigation.

The efficient removal and recovery of arsenic from copper smelting flue dust have received widespread attention due to its extremely high toxicity and carcinogenicity. In this research, a roasting method used for treating the dust at a relatively low temperature (300-400 â„ƒ), with adding sulfuric acid and bitumite, was proposed, in which the reduction of As(Ⅴ) and oxidation of arsenic sulfides were achieved simultaneously. It was proved by thermodynamic analysis and experiments that adding sulfuric acid was favorable for the removal of arsenic, through enhancing the thermodynamic driving force and promoting the transformation of arsenate and arsenic sulfides to As2O3. The phase transformation of arsenic was analyzed using XRD, SEM-EDS and XPS, which indicated that coal addition, roasting temperature and H2SO4 dosage play essential roles in arsenic removal. Based on the lab-scale experiments, the optimal conditions for arsenic removal were found to be at the roasting temperature of 300-400 °C, roasting time of 2-3 h, coal addition of 5% and H2SO4 dosage of 0.2-0.3 mL/g. Around 98% of arsenic was volatilized from the dust, while arsenic content in the residue was decreased to 0.57%. Eventually, arsenic was recovered as As2O3 with a high purity of 99.05%.

A simple and effective process for recycling zinc-rich paint residue.

Continuous growth of the shipping industry and infrastructure has consumed large amounts of zinc-rich paint (ZP) for the protection of steel structures against corrosion. Consequently, a growing amount of waste zinc-rich paint residue (ZPR) is being generated from anticorrosion spraying. ZPR is classified as hazardous waste in most industrialized countries, but it contains considerable amounts of organic compounds with high calorific value and zinc species that can potentially be recycled. Most of the ZPR generated is not properly treated, and this study presents a simple and efficient process for recycling ZPR. The zinc in ZPR was recovered via a hydrometallurgical route through oxidative alkaline leaching and electrowinning. The results show that the leaching ratio of zinc was greater than 98% at 95 °C, NaOH concentration of 250 g/L, liquid/solid ratio of 10:1, air flow rate of 0.6 L/min, and leaching time of 1.5 h. The appropriate minimum concentration of zinc for electrowinning was determined to be 10 g/L. Adding 50 mg/L of gelatin to the electrolyte significantly refined the grain and the optimum current density was determined to be 200 A/m2. Fern shaped cathode zinc powders with a purity of 99.8% were obtained. A high current efficiency (92.7%) was also obtained with energy consumption of 2330.3 kWh per ton of zinc produced. The composition and thermal analysis of the leaching residue suggest that co-processing in cement kiln may be suitable for disposing the leaching residue of ZPR. The experimental results show that the proposed process is promising for ZPR recycling.

Cleaning of lead smelting flue gas scrubber sludge and recovery of lead, selenium and mercury by the hydrometallurgical route.

The expansion of the nonferrous metal smelting industry in the recent two decades has resulted in the generation of massive quantities of flue gas scrubber sludge containing hazardous heavy metals, such as cadmium, lead, arsenic, selenium and mercury (Hg), posing a potential environmental threat. In this work, lead smelting flue gas scrubber sludge was treated by a hydrometallurgical process to achieve sludge cleaning and economic recovery of metal values lead, selenium and mercury. The sludge was preliminarily leached by sodium chloride solution to extract lead. Under the optimum conditions, 99.8% of lead was selectively leached into the solution and subsequently precipitated by calcium oxide while almost the entire selenium and mercury remained in residue. Ninety-eight percent of selenium and 99.8% of mercury were further leached by hydrochloric acid solution with sodium chlorate. 99.3% of mercury was precipitated as red mercuric oxide from the Se-Hg leach liquor by adding sodium hydroxide. After the mercury was removed from the solution, 97.5% of selenium was reduced and precipitated as crude selenium by reduction with sodium sulfite. Recovery yields of lead, mercury and selenium by this process were 99.6%, 98.9% and 95.5%, respectively.

Mechanism of sodium chloride in promoting reduction of high-magnesium low-nickel oxide ore.

Sodium chloride has been proved that it is an effective promoter for the reduction of high-magnesium, low-nickel oxide ore. The aim of current work is to clarify the promotion behavior of sodium chloride in the roasting reduction process. The influence of moisture on the reduction of ore in the presence of sodium chloride is studied to get clear comprehension of promotion process. In the presence of moisture, the HCl is produced by pyrohydrolysis of sodium chloride for chlorinating nickel and iron oxides, moreover, interactions between metallic oxides and sodium chloride are also a way for chlorination at high temperature (>802 °C); subsequently, the metal chloride would be reduced by reductant. In the absence of moisture, the magnetic separation results show that the recoveries of iron and nickel have a significant increase; moreover, olivine structure would be destroyed gradually with the increase of roasting temperature in the action of sodium chloride, and the sodium chloride existed in high-magnesium, low-nickel oxide ore could make the NiO isolate from NiO-bearing minerals. The NiO reacts with Fe2O3 at high temperature to form NiFe2O4, which is conductive to the formation of Ni-Fe alloy during the reduction process.