Extraction of valuable metals from low nickel matte by calcified roasting−acid leaching process

A calcified roasting−acid leaching process was developed as a highly effective method for the extraction of valuable metals from low nickel matte in the presence of CaO additive. The influences of process parameters on the metal extraction were studied, including the roasting temperature, roasting time, addition of CaO, H₂SO₄ concentration and liquid−solid ratio. Under the optimum condition, 94.2% of Ni, 98.1% of Cu, 92.2% of Co and 89.3% of Fe were recovered. Additionally, 99.6% of Fe was removed from the leachate as goethite by a subsequent goethite iron precipitation process. The behavior and mechanism of CaO additive in the roasting process was clarified. The role of CaO is to prevent the formation of nonferrous metal ferrite phases by a preferential reaction with Fe₂O₃ during the roasting process. The metal oxides (CuO and Ni_xCu_1−xO) remained stable during high-temperature roasting and were subsequently efficiently leached using a sulfuric acid solution.     

The oxidation of nickel—tungsten alloys

The oxidation behaviour of NiW alloys and NiWCr alloys containing up to 40 wt%W has been studied in the temperature range 900–1200°C. The parabolic rate constant for oxidation increases with increasing tungsten content in the alloy. Addition of 10 or 15%Cr causes a significant reduction in the oxidation rate.In the Ni—7·5W alloy, spherical internal oxide particle of WO₃ are formed within the alloy, whereas as the tungsten content is increased the tendency to internal oxidation diminishes but the alloy/scale interface develops a highly irregular morphology. The roughened alloy/scale interface is less marked at the higher oxidation temperatures, and also when chromium is present in the alloy. The morphology of the interface is probably related to the relatively low interdiffusion coefficient in NiW alloys.     

Removal of magnesium and calcium from electric furnace titanium slag by H3PO4 oxidation roasting–leaching process

H₃PO₄ oxidation roasting followed by HCl acid leaching was proposed to remove magnesium and calcium from electric furnace titanium slag containing 3.12% MgO and 0.86% CaO. XRF, XRD and SEM techniques were used to characterize the composition, mineral phase component and microstructure of the titanium slag. The H₃PO₄ oxidation thermodynamic, mineral phase transformation, microstructure, element distribution in titanium slag during H₃PO₄ oxidation process and leaching process were investigated. The thermodynamic analysis indicated that H₃PO₄ could promote the decomposition of MgTi₂O₅ and CaSiO₃. The results indicated that H₃PO₄ could effectively promote the transformation of titanium-bearing mineral to rutile and enrich the impurities in M_xTi_3–xO₅ into phosphate which could be removed by acid leaching process. Under the studied conditions, the leaching rates of magnesium and calcium reached 94.68% and 87.19%, respectively. The acid leached slag containing 0.19% MgO and 0.13% CaO (mass fraction) was obtained.     

Continuous and directional solidification technology of titanium alloys with cold crucible

The experiments of continuous and directional solidification of titanium alloys with cold crucible were carried out in a multifunctional electromagnetic cold crucible apparatus. Parameters and factors influencing the surface crack and macrostructure of titanium alloy ingots were studied. The mechanism of the parameters and factors influencing the surface crack and macrostructure of the ingots were interpreted. The results show that the surface cracks of the prepared ingots decrease with the increase of the input power from 50 to 60 kW or with the increase of the coil turns from 3 to 5 circles. The surface cracks increase with the increase of withdrawal velocity from 3 to 5 mm/min or the height of the primer from 2 to 3 cm, then decrease with the increase of withdrawal velocity from 5 to 8.7 rnm/min or the height of the primer from 3 to 4 cm. Coil turns is the most important one in all parameters effect on the surface crack, the input power is more important, then the withdrawal velocity is important and the height of the primer is the least important. Withdrawal velocity is the most important factor affecting the macrostructure, and effects of other factors on maerostructure is slight. With the decrease of velocity from 8.7 to 0.5 mm/min, the quantity of grains reduces, the grain orientation degree becomes small, and the solidification fronts change from concave to plane to convex. The ingot can be directional solidified at velocity of 1 mm/min. The ingot with free surface crack and directional macrostructure is prepared under definite conditions.     

Dissolution mechanism of solid nickel in liquid zinc saturated with Fe

The dissolution behavior of solid nickel in static liquid zinc saturated with Fe at 723 K was studied. The results show that when immersing solid Ni in liquid Zn saturated with Fe, the intermetallic compound layers consisted of γ and δ phases are formed on nickel substrate, which is the same as that in liquid pure zinc. However, some F2 particles are formed in the liquid near the solid/liquid interface. These Г2 particles can easily heterogeneously nucleate on （particles and grow fast. The dissolution process is governed by diffusion of nickel atom across a concentration boundary layer in liquid Zn saturated with Fe, and is different from a mixed control mechanism of nickel in liquid pure zinc. The participation of Г2 particles makes the dissolution of solid Ni in the liquid accelerated.     

Technological prrogress on detoxification and comprehensive utilization of chromium—containing slag

Chromium salt is an important industrial material,but vast waste slag containing chrome(Ⅵ）is brought out in the process of its production.The slag in seriously harmful to environments and human health.The technologies on detoxification and comprehensive utilization of chromium-containing slag were summarized abroad and at home.And various methods were also described for the detoxification mechanism,technology process,and pactical application effects in detail.A new concept for detoxification of chromium-containing slag,furthermore,was put forward by using microorganism.     

Continuous generating grinding—Tooth root machining and use of CBN-tools

Profile accuracy, no burning and residual compressive stresses at the tooth root fillet are required for the durability of highly stressed gears. This paper reveals the challenges for continuous generating grinding with corundum and CBN. For this purpose, material removal simulations and experimental investigations were carried out to gain knowledge of the tool–workpiece contact conditions. The potential of CBN tools was analysed due to the fact that the mechanical loads at the grinding worm tip result in high profile wear of the corundum tools. In this context, especially the interrelationship between the dressing strategy and the workpiece quality was investigated in detail.     

Kinetics and mechanism of the nickel electrode—II. Acid solutions containing a high concentration of sulphate and nickel ions

The kinetics of the Ni electrode in acid solutions with a high sulphate and nickel ion concentration has been investigated in the range of 25–75°C. The active dissolution and the passive regions and the active-passive transition phenomena have been studied employing different potential perturbation techniques using both still and stirred solutions.Two electrochemical processes are competing within the prepassive film potential region, namely, the active Ni dissolution to Ni(II) ions and the Ni(OH)₂ film formation. Nickel passivation is explained by reaction pathways involving successive electrochemical and chemical steps implying the occurrence of hydroxo- and oxo-species as reactions intermediates. The advanced mechanism is based upon a positively charged Ni surface structure and attributes the onset of the complete passivity to a particular surface oxide species.     

Separation of cadmium and nickel from waste Ni—Cd batteries

To separate the cadmium and nickel resources in waste Ni-Cd batteries,a self-designed vacuum distillation recycling system was studied under laboratory conditions.The effects of system temperature,operating pressure,and time on the separation of Ni and Cd were studied respectively.The mechanism of vacuum thermal recycling was also discussed.Results show that vacuum distillation is a very effective separation method for waste Ni-Cd batteries.At a Constant pressure,the increase of temperature can improve the separating efficiency of Cd.When the temperature is 1173K,Cadmium can evaporate completely from the samples during 3h at 10Pa,The reduction of pressure in a certain range is effective to the separating of Cd from Ni-Cd batteries by vacuum distillation.     

Continuous electric resistance heating—Hot forming system for high-alloy metals with poor workability

A new hot forming system for high-alloy metals with poor workability is developed. This forming system is a direct combination of a forming machine and continuous electric resistance heating, and is capable of the high-speed forming of metals with flexible and precise control of elevated temperature. The prototype of the new forming system is applied to the forming of high-alloy metals with poor formability, such as a Ti–6Al–4V bar, and the basic characteristics of this forming system are clarified. Using this system, sound, high speed forming of high alloys becomes possible, and the Ti–6Al–4V bar is successfully formed without fracture.     

Dislocation configurations and stress-corrosion properties of alloys in the nickel—chromium—iron system

Abstract

Stress-corrosion tests have been performed in sodium chloride at 300° on commercially produced and laboratory-made nickel alloysand austenitic steels. It has been found that resistance to transgranular stress corrosion cracking depends upon the (Ni + Cr) content. Commercial high-Ni alloys are resistant, as are relatively pure Ni–Cr–Fe alloys with (Ni + Cr) ≥ 50% wt. The resistance of alloys with approximately 20% Cr and 20—40% Ni is markedly influenced by other alloying elements, for example, silicon and molybdenum.

Electron microscope studies indicate that resistance to cracking can be approximately correlated with the extent to which dislocation ‘tangling’ occurs at a particular deformation. Planar dislocation arrays appear to be a necessary, though not sufficient,condition for susceptibility. It is thought that the observed dislocation arrangements can be understood without recourse to hypotheses of ordering in these alloys. The influence of some alloying elements, e.g. chromium and silicon, cannot be interpreted simply in terms of their influenceon dislocation arrangements. The favourable effectof these elementson resistance to stress-corrosion cracking is probably associated withtheir ability to increase the protective properties of surface oxide films and thus to inhibit the crack initiation process.     

The passivation of nickel in aqueous solutions—I. The identification of insoluble corrosion products on nickel electrodes using optical and ESCA techniques

In situ differential reflectometry in conjunction with ESCA techniques are used to identify various surface films which form electrochemically on nickel. The film observed on pure Ni in a 0.15 N Na₂SO₄ electrolyte has been identified to be primarily Ni(OH)₂. At different values of pH and potential, NiO has been found to form simultaneously with Ni(OH)₂. At solutions with pH > 8, the Ni(OH)₂ film partially transforms into a third oxide, presumably NiOOH, which can only be observed in situ.     

Development of the Process Index for NiCrAlY Coatings with the Mettech Axial III™ System

NiCrAlY coatings were deposited using the Mettech Axial III? plasma spray system. The microstructural features of the coatings, such as the porosity, crack, un-melted particle, and oxide content, were analyzed to investigate the effects of the spray process parameters on these features. Two Taguchi arrays were used to examine the effects of the spray process parameters such as powder size, ratio of (H₂ + N₂) gas flow over total gas flow, current, spray-gun nozzle size, and spray distance, on the microstructural features of the coatings. The results from statistical analysis are used to create regression equations to predict the microstructural features of the coatings. In the regression equations, a process index (PI) is used as a complex variable incorporating a number of process parameters. The results from an additional set of experiments are used to verify the validity of the regression equations. It has been demonstrated that the equations correlate well with the results from the subsequent set of experiments. It is concluded from this study that the PI can be used to categorize coating qualities with respect to the extent of crack, porosity, unmelted particle, and oxide content in the coating. These equations can also serve as an initial step in developing process parameters by means of the Mettech Axial III? System.     

Sol–gel coating treatment of SiC particles and properties of resulting nickel/SiC composites

Abstract

Nickel matrix composite layers reinforced with SiC particles have been widely used for the protection of friction parts, combustion engines and casting moulds, due to their high specific strength and excellent wear resistance. Both the nickel and the SiC particles also have excellent high temperature performance. Unfortunately, interfacial reactions between nickel and SiC occur at temperatures above 450°C, leading to deterioration of interfaces with a sharp decline in high temperature properties.     

Codeposition of nickel–phosphorus alloys reinforced with boron carbide microparticles: direct and pulse plating

Nickel–phosphorus alloys were codeposited with boron carbide particles. Two compositions of nickel-phosphorus, one presenting a low phosphorus content in the order of 4% wt. and another one presenting a high phosphorus content of about 12% wt., were deposited from modified Watts nickel electrolytes using both direct and pulse plating. A strong influence of the deposition method was observed on the phosphorus content in the matrix and on the quantity of codeposited particles. Pulse plating was found to significantly increase both of them. Nucleation of the pure nickel–phosphorus alloy and of the codeposit were studied using chronoamperometry and AFM in potentiostatic mode. An instantaneous nucleation mechanism was evidenced on iron and gold substrates. Microhardness was measured and linked to the phosphorous and particle contents.