Fuming Furnace Research Articles

Improved Settling Mechanisms of an Industrial Copper Smelting Slag by CaO Modification

A significant source of copper losses from pyrometallurgical copper extraction is attributed to dissolved and entrained copper in discarded slag. Entrained copper can be recovered via pyrometallurgical slag cleaning in a settling furnace, where the slag viscosity and copper droplet size distribution (CDSD) are critical parameters. Reduced copper losses suggest improved raw material efficiency, and the slag becomes a more environmentally safe byproduct. In this study, iron silicate slags from a smelting furnace are industrially CaO modified in a fuming furnace to contain a CaO content between 8 and 18 wt.%. The viscosity of slags with and without CaO modifications is evaluated in the temperature range from 1423 to 1723 K. The influences of the CaO modifications on the CDSD, slag matrix copper content, and total copper content were determined. The results show that the slag viscosity decreases with increasing CaO concentrations in the slag. In addition, the copper content decreases in the slag phase, and the CDSD shifts to contain relatively larger droplets. The effect of CaO slag modification reveals a linear relationship between the overall copper recovery and viscosity, which increased from 63 to 88% when the viscosity in the respective batch was 0.51 and 0.25 Pa·s.Graphical

Potential Investigation of Stabilised Fuming Furnace Slag for Road Construction

Fuming furnace (FF) slag is one of the industrial waste materials which is generated during extraction of zinc metal at the zinc industry. It is deposited at the designated FF slag yard near the plant area with very limited use. As a result, the deposits are increasing year after year posing threat to the environment and occupying large area of precious land. The present research explores the possibility of using this waste material in the road construction. The tests like Scanning electron microscope (SEM), Energy dispersive spectrometer (EDS) and X-ray diffraction was carried out on FF slag. To improve its geotechnical properties, it was mechanically stabilised with jarofix (another waste material generated from the same zinc industry) in the range of 25 to 75 percent. Apart from compaction characteristics, shear strength and consolidation characteristics of these mixes were studied to conclude about its feasibility in embankment and granular layers of road pavement. These mixes were further chemically stabilized with cement in the range of 3 to 9 percent to investigate their potential application in sub base and base layers of road construction. Compressive and durability characteristics of these mixes were also studied. Detailed laboratory study concluded that FF slag is a porous; amorphous cohesionless coarse grained material with high angle of internal friction. Engineering properties viz. dry density, CBR, and shear strength characteristics improved significantly after mechanical stabilisation with jarofix. These parameters of FF slag were compared with other industrial waste materials. Unconfined compressive strength and durability characteristics indicated suitability of cement stabilised slag-jarofix mixes for sub base and base layers of road pavement. It was concluded that about 20-30 percent of FF slag can be used as a replacement of fine aggregate in these granular layers. A typical pavement design indicated that it is possible to reduce the total pavement thickness of about 13 percent by using cement stabilised slag-jarofix mix.

Settling of Copper Phases in Lime Modified Iron Silicate Slag

Copper in discarded slag decreases the profits and copper recovery during the pyrometallurgical extraction processes. The copper losses to slag can be reduced by using a settling furnace, in which mechanically entrained copper droplets separate from the slag under the action of gravity. The settling rate of entrained droplets can be increased by modifying the slag composition and, thus, the slag properties, which are known to influence the settling rate. The knowledge of industrial CaO slag modification in a reduced iron silicate slag with a Fe/SiO2 ratio close to unity is limited. An industrial trial was thus conducted in an electric settling furnace, where the slag had been pretreated in a fuming furnace, to investigate the effect of CaO slag modification on the final slag copper content. Slag samples were collected from the ingoing and outgoing slag and from within the furnace of batches modified with CaO up to about 16 wt %. The trial was evaluated by comparing the final slag copper content and the copper recovery in the settling furnace. The results indicate that the settling becomes more efficient with the CaO modification as the final slag copper content decreased with increasing CaO content.

Design and implementation of an energy-saving melting reactor

A physico-chemical model of zinc recovery, in the melt ideal mixing regime, has been developed. From the cold model experiments, the melt complete mixing time criterial equation is derived. Based on it, the parameters of pilot plant were calculated and consequently the experiments for validation were conducted. The value of specific volumetric productivity, which is the key factor for calculation of the industrial sample of the reactor has been determined. By the method of affine modeling, test results of the pilot plant on its industrial design were recalculated. The calculation results demonstrate that by the increase of reactor slag productivity from 0.693 t/h up to 30 t/h, the share of the effectively used heat will increase, the heat share of the cooling water will be decreased and the fuel consumption will be reduced approximately by 2.5, 2.7 and 3 times respectively. Furthermore, by processing of solid slag, the fuel consumption would be reduced by 1.5 times compared to the one in the fuming furnace processing melted slag. It would also be 3–4 times lower than waelz-kiln treating the granulated slag. Due to low level of the molten bath in the reactor where the height is about 0.2 m, the power consumption of the air blower would be approximately 2 times less than that in fuming furnace of height about 0.7 m.

Utilisation of lead–zinc mill tailings and slag as paste backfill materials

Paste backfilling is an incipient underground mine backfill technology in India. It facilitates maximum use of mill tailings with enhanced stability of the underground workings and minimises rehandling of water, as well as provides bulk disposal of mining solid waste. Binder type and dosage plays an important role in paste backfill performance. This paper highlights environmentally friendly utilisation of solid wastes like lead–zinc mill tailings and lead–zinc smelter fuming furnace slag (FFS) as paste backfilling for an underground metalliferous mine. Various experiments were conducted to study the effect of use of FFS as a fractional replacement for ordinary portland cement (OPC) in paste backfilling. The physico-chemical properties of both the lead–zinc mill tailings and fuming furnace slag (FFS) have been examined. In the first set of experiments, raw slag (FFS) was used for paste backfill preparation and experimentation for uniaxial compressive strength (UCS) development, whereas in the second set of experiments, FFS was crushed to -75 μm (80 wt%) and used for the study. Multiple regression analysis of strength development was also conducted up to fifth order. The regression analysis is in accordance with the strength development and justifies the significance of OPC, crushed fuming furnace slag (CFFS) and waste chemistry on the strength gain with curing time. Use of crushed fuming furnace slag as OPC replacement in paste backfill showed encouraging results of strength development in contrast to raw FFS. Also, the economic analysis revealed that the paste backfilling cost per tonne reduced significantly with slag replacement in the binder phase.

Prediction Model of Smelting Endpoint of Fuming Furnace Based on Grey Neural Network

Since grey theory and neural network could improve prediction precision, the technology of combination prediction was proposed in this study. Then the algorithm was simulated by Matlab using practical data of a fuming furnace. The results reveal that the smelting endpoint of fuming furnace could be accurately predicted with this model by referring to small sample and information. Therefore, GNN model is effective with the advantages of high precision, fewer samples required and simple calculation.

Removal of F and Cl from Zinc Oxide Fume from Fuming Furnace by Microwave Roasting

The work addresses the removal effectiveness of F and Cl in the zinc oxide fume produced in fuming furnace, by application of microwave roasting, taking advantage of the difference in microwave absorbing characteristics of halides, lead and zinc oxides in combination with the advantage of selective microwave heating. The effectiveness of defluorination and dechlorination was discussed in detail addressing the effect of all the influencing parameters such as roasting temperature, holding time and stirring speed. SEM and XRD were utilized to understand the removal mechanism of F and Cl. The results show that a nearly 92.8 % defluorination efficiency and 90.3 % dechlorination efficiency could be achieved at roasting temperature of 700 °C, holding time of 80 min and stirring speed at 120 rpm, satisfying the requirements of the wet smelting electrolysis process.

Response surface optimization of process parameters for the removal of F and Cl from zinc oxide fume by microwave sulphating roasting

Microwave sulphating roasting was applied to zinc oxide fume from a fuming furnace for the removal of F and Cl. The effect of important parameters such as roasting temperature, holding time. and vapour flow were investigated and the process conditions were optimized using response surface methodology. The results showed that the effects of roasting temperature and holding time on the removal efficiency of F and Cl were most significant, and the effect of vapour flow is of much lower importance. The defluorination and dechlorination efficiency increased rapidly as the roasting temperature and holding time increased, while the vapour flow had little effect. The defluorination efficiency could reach 91.3% while the dechlorination efficiency could reach 89.5%, under the process conditions of roasting temperature 655°C, holding time 65.2 minutes, and vapour flow of 6.8 ml/min. The results showed that the removal of F and Cl from zinc oxide fume using a microwave direct roasting process is feasible and reliable.

95/05387 Prevention of coal dust explosions in the fuming furnace

95/05387 Prevention of coal dust explosions in the fuming furnace

Heat-transfer phenomena in water-cooled zinc-fuming furnace jackets

In the zinc slag-fuming process, zinc is removed from lead blast furnace slag by reduction with a coal-air mixture injected into the slag through submerged tuyeres. The furnace is constructed of water-cooled jackets which freeze a slag layer and contain the bath. This greatly reduces vessel wear caused by the violently agitated and corrosive bath. The jackets, however, fail due to the formation of cracks which grow from the slag face through the working face of the jacket to the water channel. In this study, in-plant measurements and mathematical modeling of heat transfer in the jackets have been combined to elucidate the mechanism of failure. The working face of a water jacket was instrumented with thermocouples and installed in a fuming furnace at the Trail smelter of Cominco Ltd., Trail, BC. Measurements revealed the presence of large thermal transients or temperature “spikes” in the panel in the region immediately above the tuyeres. These were generally observed during charging and tapping of the furnace and are likely associated with disturbances on the surface of the bath or gas injection effects when the liquid level is low. Temperatures at the midthickness were seen to rise by as much as 180 °C above the steady-state level. Under these conditions, low-cycle fatigue may lead to crack formation and propagation. A mathematical modeling analysis of the transient freezing phenomena indicates that the temperature spikes are associated with sudden slag falloff and direct contact of molten slag on the jacket. In order to reduce slag falloff, an increased number of anchoring fins should be used in critical areas.

Kinetics of the zinc slag-Fuming process: Part i. industrial measurements

A study involving industrial measurements and mathematical modeling has been conducted to eluci-date kinetic phenomena in the zinc slag fuming process. In the first part of this three-part paper, the results of industrial measurements and observations are presented. In Part II a mathematical model of the process is developed, and finally in Part III the implications of a kinetic conception of the process for process improvement are explored. The industrial work consisted primarily of slag sampling through the fuming cycles of five different fuming operations. In addition, tuyere back-pressure mea-surements, tuyere photography using a tuyerescope, and sampling of the fume product were under-taken at one operation. Analysis of the slag samples has shown that, in general, the zinc elimination curve is linear with time and that a portion of the injected coal entrains in the slag. Analysis of tuyere back-pressure fluctuations and movie photographs of the tuyere tip indicate that the coal-air mixture enters the slag in the form of discrete bubbles. From these results it can be deduced that the fuming furnace consists of two reaction zones which are created by the division of coal between the slag and the tuyere gas stream. The coal entrained in the slag reduces ZnO and Fe3O4 in a “reduction zone” which is responsible for fuming. The coal remaining in the tuyere gas stream combusts in an “oxidation zone” although a fraction passes through the bath unconsumed and reports to the solid products. The oxidation zone supplies heat to the endothermic reduction reactions and heat losses.

Injection phenomena in nonferrous processes

Injection phenomena in a Peirce-Smith copper converter and a slag fuming furnace have been investigated during blowing. A tuyerescope attached to the back of a given tuyere has been employed to observe the build-up, and to obtain samples, of accretions while a piezoelectric transducer has been used to measure pressure fluctuations in the tuyere. It has been found that in both processes the accretions grow upward by a freezing mechanism from the bottom of the horizontal tuyere. Probing the shape of an accretion in the fuming furnace, without coal injection, showed that the accretion grew into the bath 30 to 40 mm from the tuyere tip. A study of the shape and frequency of the pressure pulses as well as the duration of intervals of low pressure in the tuyere has revealed that the closely spaced tuyeres may operate independently or may interact. Tuyeres in a full slag fuming furnace act independently of one another, and the air discharges in the classical bubbling regime at 5 to 6 bubbles per second. In the copper converter there is more tuyere interaction as bubbles growing at adjacent tuyeres coalesce to form a horizontal unstable gas envelope. In both processes if the tuyeres are shallowly submerged the gas may channel directly to the surface without forming bubbles. The influence of bath viscosity, the extent of wall erosion at the tuyere line, and tuyere submergence on these injection phenomena have been elucidated qualitatively.