Analysis of the Characteristics of Materials Obtained by Recycling Scrap Metal in Guinea

The aim of this study was to determine the quality of rebar produced from recycled scrap metal collected throughout the country,and imported rebar sold in the Republic of Guinea.To do this,the samples were subjected to various mechanical tests involving traction,bending and microscopic analysis.In the Lambanyi and Casse Sonfonia samples,all the tensile strength values for diameters 12,14 and 16 were above 550 MPa.Conversely,the iron samples from Baillobaye and the 10 mm diameters of the samples from Casse Sonfonio and Lambanyi have less appreciable values.The limits of elasticity were determined.The various values found vary more or less from the conventional yield strength of the NF A35-016 reference supplied by CBITEC,which is 500 MPa.Microscopic analysis gives us an insight into the internal structure of the iron samples used.This study may provide the company and the vendors with an alternative for their improvements.

Co-pyrolysis of soybean soapstock with iron slag/aluminum scrap,and characterization and analysis of their products

Soybean soapstock(SS) is one of the main solid wastes produced in the refinery of edible oil processing. In this study, the co-pyrolysis of SS with iron slag(IS) and aluminum scrap(AS) was carried out in a tubular furnace. The gas, liquid and solid products were characterized and the char yield decreased with increasing IS/AS ratio. IS and AS can improve the gas yield, and when the ratio of SS/IS was 1:0.25, the total pyrolysis gas and hydrogen contents were significantly increased. The content of oxygen compounds in pyrolysis oil decreased during co-pyrolysis, while AS promoted the content of polycyclic aromatic hydrocarbons in pyrolysis oil. The co-pyrolysis reaction can be divided into four stages, the mass loss rate reaches the maximum at the third stage(390–575 ℃). The molar ratio of H/C was lower for pyrolysis,indicating good stability of pyrolysis char owing to the high degree of carbonization and aromaticity.The possible co-pyrolysis reaction mechanism was explored.

Discussion on Abnormal Corrosion and Material Selection of Hot Iron Ladles with Steel Scrap Addition

The abnormal corrosion of hot iron ladles was investigated.The performance,the composition and the structure of bricks for hot iron ladles were analyzed.The results show that(1)compared with the alumina-silicon carbide-carbon bricks for the ladle bottom,those for the ladle wall have more pyrophyllite and the Al2O3 content of 36.32 mass%;their bulk density,apparent porosity and cold compressive strength are lower than the requirement of industry standard;they have poor anti-oxidation performance and are oxidized to form a porous layer during service,which loosens the brick lining structure thus leading to fracture,local wear and structural damage of bricks;(2)without preheating,steel scraps are not completely melted,resulting in slag or steel attachment at the mouth or the bottom of ladles thus increasing damage of ladles;(3)and the residual bricks react with the attached slag to form low melting point phases affecting their hot properties.The refractories for the lining of hot iron ladles must be improved in combination with process changes,not entirely by raw materials replacement to reduce costs.

Derived oil production by catalytic pyrolysis of scrap tires

Scrap tires were pyrolyzed in a continuously stirred batch reactor in the presence and absence of catalysts. The maximum yield of derived oil was up to 55.65 wt%at the optimum temperature, 500 °C. The catalytic pyrolysis was performed using 1.0 wt%（on a scrap tire weight basis） of catalysts based on ZSM‐5, USY,β, SAPO‐11, and ZSM‐22. The oil products were characterized using simula‐tion distillation, elemental analysis, and gas chromatography‐mass spectrometry. The results show that using a catalyst can increase the conversion of scrap tires to gas and decrease char by‐products;the yield of derived oil remains unchanged or a little lower. The oils derived from catalytic pyrolysis had H/C ratios of 1.55–1.65 and contained approximately 70–75 wt%light oil, 0.3–0.58 wt%S and 0.78–1.0 wt%N. Catalysts with high acid strengths and appropriate pore sizes, such as ZSM‐5, USY,β, and SAPO‐11, increased the amount of single‐ring aromatics in the light‐middle‐fraction oil to 45 wt%. The derived oil can therefore be used as a petrochemical feedstock for producing high‐value‐added chemical products or fuel oil.

Effect of extrusion ratio on microstructure and mechanical properties of AZ91D magnesium alloy recycled from scraps by hot extrusion

A method for recycling AZ91D magnesium alloy scraps directly by hot extrusion was studied.Various microstructural analyses were performed using the techniques of optical microscopy,scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).Microstructural observations revealed that all the recycled specimens consisted of fine grains due to the dynamic recrystallization.The main strengthening mechanism of the recycled specimen was grain refinement strengthening and homogeneous distribution of oxide precipitates.The interfaces of individual scraps of extruded materials were not identified when the scraps were extruded with the extrusion ratio of 40-1.Oxidation layers of the scraps were broken into pieces by high compressive and shear forces under the extrusion ratio of 40-1.The ultimate tensile strength and elongation to failure increased with increasing the extrusion ratio.Recycled specimens with the extrusion ratio of 40:1 showed higher ultimate tensile strength of 342.61 MPa and higher elongation to failure of 11.32%,compared with those of the cast specimen.

Recycle for Sludge Scrap of Nd-Fe-B Sintered Magnet as Isotropic Bonded Magnet

The reduction diffusion method was performed for the sludge scrap of Nd-Fe-B sintered magnets with adding Ca metal to recover the oxidized Nd-Fe-B phase. After washing the resultant powders to remove Ca metal component, the powders obtained were recycled as an isotropic magnetic powder by the melt spinning method. The magnetic properties of powders as recycled were inferior, especially for the coercivity value, due to the deletion of rare earth metals during the washing process. The adjustment of metal composition, i.e., the addition of Nd metal, at the melt spinning process improved the magnetic properties to be B r=～0.75 T, H cj=～0.93 mA·m -1, and (BH) max=～91 kJ·m -3. The magnetic properties of the bonded magnets prepared from the composition-adjusted powders were B r=～0.66 T, H cj=～0.92 mA·m -1, and (BH) max=～70 kJ·m -3, which are approximately comparable to the commercially available MQPB boned one (B r=～0.73 T, H cj=～0.79 mA·m -1, and (BH) max=～86 kJ·m -3).

RECOVERY OF CADMIUM AND NICKEL FROM SCRAP Ni-Cd BATTERIES

Several typical methods for the recovery of Ni-Cd batteries are described in detail. Based on the comparison between the hydrometallurgical process and the pyrometallurgical process, the latter is selected as the suitable method for recycling Ni-Cd batteries in China.

Crushing performance and resource characteristicof printed circuit board scrap

The crushing performance of printed circuit board (PCB) was studied on several crushers. The results show that PCB is a material which is difficult to crush. The crushing performance of PCB with disk crusher, especially vibration grinding, which has cut or impact action, excels that of jaw crusher or roller crusher. The PCB scrap is worthwhile to recycle using variety of modern characterization methods. When compared with natural resources, this material stream remains a rich precious metal and nonferrous metals. In PCB scrap, metals account for 47% of the total material composition, in which there exists 19.66% copper, 11.47% iron, 3.93% lead, 300 g/t gold and 510 kg/t silver, etc. In addition, the PCB scrap contains 27% of plastics and 26% of refractory oxides.

Effect of Mn addition and refining process on Fe reduction of Mg−Mn alloys made from magnesium scrap

The Fe reduction,microstructure evolution and corrosion susceptibility of Mg−Mn alloys made from magnesium scrap refining with Mn addition were investigated.The results show that significant Fe content change occurs during near-solid-melt treatment(NSMT)process even in the absence of Mn,because of the high saturation of Fe in the melt.Furthermore,in the NSMT process,even a small amount of Mn addition can lead to a sharp deposition of Mn atoms.The NSMT process can increase the growth rate of the Fe-rich particles,and then accelerate their sinking movement.Nevertheless,the addition of Mn hinders the coarsening process of Fe-rich particles.Besides,the corrosion susceptibility of the alloys is mainly affected by the solubility of Fe,which can be significantly reduced by Mn addition.Moreover,the presence of more Fe-rich particles does not necessarily increase the corrosion susceptibility of the alloy.Consequently,in the refining process of Mg−Mn alloys made from magnesium scrap,on the basis of NSMT process and adding an appropriate Mn content(about 0.5 wt.%),the purity of the melt can be improved,thereby obtaining an alloy with excellent corrosion resistance.

Simulation on scrap melting behavior and carbon diffusion under natural convection

A 3D model applying temperature-and carbon concentration-dependent material properties was developed to describe the scrap melting behavior and carbon diffusion under natural convection.Simulated results agreed reasonably well with experimental ones.Scrap melting was subdivided into four stages:formation of a solidified layer,rapid melting of the solidified layer,carburization,and carburization+normal melting.The carburization stage could not be ignored at low temperature because the carburization time for the sample investigated was 214 s at 1573 K compared to 12 s at 1723 K.The thickness of the boundary layer with significant concentration difference at 1573 K increased from 130μm at 5 s to 140μm at 60 s.The maximum velocity caused by natural convection decreased from 0.029 m·s^(−1)at 5 s to 0.009 m·s^(−1)at 634 s because the differences in temperature and density between the molten metal and scrap decreased with time.

Microstructure and Mechanical Properties of AZ91D Magnesium Alloy Recycled from Scraps by Hot-press/extrusion

A large number of scraps are produced in the fabrication process of magnesium alloy products. It is necessary to recycle these scraps for the development and scale application of magnesium alloys. In this research,a method for recycling AZ91D magnesium alloy scraps fabricated by hot-press / extrusion was studied. Mechanical properties and microstructure of the recycled specimens were investigated. Microstructural analyses were performed by using the techniques of optical microscopy and scanning electron microscopy. Microstructural observations reveal that the recycled specimens consisted of fine grains when adopting the extrusion temperature of 400- 450 ℃,the extrusion ratio of( 25- 100) ∶ 1 and the extrusion rate of 0. 10- 0. 20 mm / s. Ultimate tensile strength and elongation to failure increased with the increase of the extrusion temperature,the extrusion ratio and the extrusion rate,respectively. Recycled specimens reached the highest ultimate tensile strength of average 361. 47 MPa and the highest elongation to failure of average 11. 55% when adopting the hot-press,the extrusion temperature of 400± 5 ℃,the extrusion ratio of 100 ∶ 1 and the extrusion rate of 0. 15 mm / s. The shape of bonding interface was tightly relation with the ultimate tensile strength. When the bonding interface formed continuous curves,the ultimate tensile strength decreased almost linearly with increasing the average width of the bonding interface. When the bonding interface formed discontinuous curves,the ultimate tensile strength increased almost linearly with the increase the proportion of the fine bonding length accounting for the measured interface length. Ultimate tensile strength of the recycled specimens could be calculated by using the forecastable equation.

Reductive denitrification of nitrate by scrap iron filings

Reduction of nitrate by zero-valent iron is a highly exergonic reaction that has long been known to occur. Use of scrap iron filings (SIF) as the PRB (Permeable Reactive Barrier) material can be used to recycle certain by-products, and identify cheaper replacements for expensive conventional PRB materials, especially pure metallic iron. The feasibility of reductive denitrification of nitrate by SIF was studied by batch experiments. Operational parameters such as pH value, SIF dosage and initial concentration of nitrate were investigated. The removal efficiency of nitrate reached 80% under the conditions of pH of 2.5, nitrate initial con- centration of 45 mg/L and SIF dosage of 100 g/L within 4 h. Results indicated that nitrate removal is inversely related to pH. Low pH value condition favors for the nitrate transformation. Different from the results of others who studied nitrate reduction using iron powder, we found that there was a lag time before nitrate reduction occurs, even at low pH. Finally, the possible mechanism of nitrate reduction by Fe0 is discussed.

Recycling of minute metal scraps by semisolid processing:Manufacturing of design materials

As a new attempt to recycle minute metal scraps, the possibility of manufacturing design materials by semisolid extrusion processing was shown.A design material with an intended shape, such as a character or petal shape, was manufactured using minute metal scraps.Similarly, a design material with an intended color pattern for each metal, such as red copper in a white aluminum matrix, resembling grainlike wood, was manufactured by mixing two or more types of minute metal scrap.In addition, secondary design materials, which have engraved patterns on the surface of the target metal made by an electric discharge machine using the above primary design material as an electrode, were manufactured.

Effect of additives on anode passivation in direct electrolysis process of copper–nickel based alloy scraps

Effects of nickel component,thiourea,glue and chloride ions and their interactions on the passivation of copper–nickel based alloy scrap anodes were investigated by combining conventional electrochemical techniques.Results obtained from chronopotentiometry and linear voltammetry curves showed that the Ni component made electrochemical stability of the anode strong and difficult to be corroded,caused by the adsorption of generated Cu2O,NiO or copper powder to the anode surface.The Ni2+reducing Cu2+to Cu+or copper powder aggravated the anode passivation.In a certain range of the glue concentration≤8×10–6 or thiourea concentration≤4×10–6,the increase of glue or thiourea concentration increases the anode passivation time.Over this range,glue and thiourea played an adverse effect.The increase of chloride ions concentration led to the increase in passivation time.

Chlorination roasting-coupled water leaching process for potash recovery from waste mica scrap using dry marble sludge powder and sodium chloride

The present paper reports the effective utilization of marble sludge powder(MSP)for the recovery of potash values from waste mica scrap using chlorination roasting-water leaching method.Characterization studies indicated the presence of dolomite as the major mineral phase in MSP,whereas muscovite and quartz were observed in the mica sample.The acid leaching studies suggest a maximum of 22%potash recovery under conditions:4 M H2SO4 acid,particle size of^100μm,stirring speed of 600 r/min,leaching temperature of 75℃,and leaching time of 90 min.The chlorination roasting-water leaching process was adopted to achieve the lowest level of 80%-90%potash recovery.The optimum conditions for the recovery of^93%potash from mica(~8.6wt%K2O)requires 900℃ roasting temperature,30 min roasting time,and 1:1:0.75 mass ratio of mica:MSP:NaCl.The roasting temperature and amount of NaCl are found to be the most important factors for the recovery process.The reaction mechanism suggests the formation of different mineral phases,including sylvite(KCl),wollastonite,kyanite,and enstatite,during roasting,which were confirmed by X-ray diffraction(XRD)analyses and scanning electron microscopy(SEM)morphologies.The MSP-blended NaCl additive is more effective for potash recovery compared with the other reported commercial roasting additives.

The Dynamic Experiment on Treating Acid Mine Drainage with Iron Scrap and Sulfate Reducing Bacteria Using Biomass Materials as Carbon Source

The study is aimed at the problem of high content of Cr^(6+),Cr^(3+)and SO_(4)^(2-)is high and low pH value in acid mine drainage(AMD).Moreover,treatment of AMD by sulfate reducing bacteria(SRB)requires the addition of carbon source,while the treating effectiveness is not good enough on its own.The sugarcane slag,the corn cob and the sunflower straw were selected as the SRB carbon source cooperating with iron scrap to construct the dynamic columns 1,2 and 3.The mechanism of removing Cr^(6+),Cr^(3+),SO_(4)^(2-)and H+and the regularity of sustained release of carbon source and TFe release was studied in AMD.The removal efficiency of heavy metal ions,the ability of sustained release of carbon source,and the ability of adjusting acid by the three dynamic columns were compared.The result shows that the average removal rates of Cr^(6+),Cr^(3+)and SO_(4)^(2-)in effluent of dynamic column 1,filled by sugarcane slag,iron scrap and SRB,were 96.9%,67.1%and 54.3%.The average release of TFe and chemical oxygen demand(COD)were 4.4 and 287.3 mg/L.Its average pH was 6.98.Compared with the performance of dynamic columns 1,2 and 3,dynamic column 1 performed best in removing Cr^(6+),Cr^(3+)and SO_(4)^(2-)from AMD and controlling the release of COD and TFe,adjusting the pH of the solution.The study is of significance in treatment of AMD by taking for biomass materials as SRB carbon source in cooperation with iron scrap.

Effect of the Proportion of Bamboo Scraps on the Properties of Bamboo Scraps/Magnesium Oxychloride Composites

This study was designed to solve the problem of large waste volume from bamboo processing residues in recent years.Using magnesium oxychloride(MO)cementitious material as the main material and bamboo residue(BR)as the reinforcing material,a BR/MO composite material was prepared.The effects of BR amount on the molding properties,mechanical strength,and water resistance of BR/MO composites were examined and discussed.Scanning electron microscopy(SEM),X-ray diffractometry(XRD),and thermogravimetric analysis were used to characterize composite microscopic morphology,crystalline structure,and heat resistance.The results showed that,when the BR content was 1.00%(by wt),the flowability of MO paste was beneficial to composite molding.Composite mechanical properties and water resistance were greatly affected by BR addition.When the BR content was 1.00%,composite compressive and bending strengths and softening coefficient all reached maximum values.Meanwhile,increases in water absorption by 24 h and decreases of contact angle were small.These results suggested that,when the BR content was 1.00%,composite mechanical properties and water resistance were the best and the mechanical strength also improved with extended composite storage time.SEM analysis indicated that BR played the role of a reinforcing phase in MO matrices.However,when the BR content exceeded 1.00%,interfacial bonding between BR and MO became less.XRD analysis showed that,with 1.00%BR content,composites showed more 5-phase crystals with high strength.This further explained the reason why this composite’s mechanical properties were the best and the heat resistance not deteriorated due to BR,which was easily decomposed.

Recovering Scrap Anode Copper Using Reactive Electrodialysis

Despite functioning without major operational problems—copper electro-refining does not allow complete use of copper anodes, peaking at 85% of the copper anode in weight. Consequently, the remaining 15% of scrap copper must be recirculated into the copper smelting. The use of reactive electrodyalysis is a system capable of continuously electro-refining scrap, by using a stainless steel basket and a cationic exchanging membrane in order to increase production of copper cathodes at the same percentage;it currently today returns to the copper smelter. In terms of specific energy consumption, this process would use between 3 and 4 times the value of normal electro-refining.

Failure Mechanisms and Structural Optimization of Shredder Hammer for Metal Scraps

Recycling retired cars can relieve the environmental pollution and resource waste efficiently.However,a few publications can be found on the failure mechanisms and optimization method of recycling equipment,shredders.Thus,the failure mechanisms and structural optimization of shredder hammers for retired cars are studied aiming improving shredding efficiency and reducing cost.Failure types of shredder hammer are studied theoretically,and it is found that wear failure and fatigue failure are the two main failure types of shredder hammer.The shredding process of metal scraps is analyzed by finite element method,and it can be divided into four stages based on the stress states：initial stage,collision stage,grinding stage and separation stage.It is proved that the shredding efficiency can be improved by increasing cutouts on the hammer head.Finally,it is determined that the hammer with two cutouts is the optimal structure for metal scraps,which can improve the shredding efficiency by 20% and lengthen the hammer life by 15%.This study provides scientific basis for the industry application and theoretical foundation for further research.

Adsorption Characteristics of Activated Carbon Derived from Scrap Tires for Malachite Green:Influence of Small Organics

The influence of small organics on the adsorption characteristics of activated carbon produced from industrial pyrolytic tire char(APTC)for malachite green(MG) was investigated by a batch method. Phenol was chosen as the representative of small organics. The effects of phenol on adsorption equilibrium, kinetics and thermodynamics were studied systematically. The results indicate that APTC is a potential adsorbent for MG. The presence of phenol decreases the adsorption capacity of APTC for MG, but improves the rate of adsorption, while the adsorption characteristics, such as equilibrium, kinetics and thermodynamics are not affected by phenol. The adsorption equilibrium data follow Langmuir isotherm and the kinetic data are well described by the pseudo-second-order kinetic model. The adsorption process follows intra-particle diffusion model and the adsorption rate is determined by more than one process. Thermodynamic study shows that the adsorption is an endothermic and spontaneous physisorption process.