Novel drying additives and their evaluation for self-flowing refractory castables

The drying step of dense refractory castables containing hydraulic binders is a critical process, which usually requires using slow heating rates due to the high explosion trend of such materials during their first thermal treatment. Thus, this work investigated the performance of alternative additives to induce faster and safer drying of self-flowing high-alumina refractory castables bonded with calcium aluminate cement (CAC) or hydratable alumina (HA). The following materials were analyzed for this purpose: polymeric fibers, a permeability enhancing compound (RefPac MIPORE 20) and an organic additive (aluminum salt of 2-hydroxypropanoic acid). The drying behavior and explosion resistance of the cured samples were evaluated when subjecting the prepared castables to heating rates of 2, 5 or 20 °C/min and the obtained data were then correlated to the potential of the drying agents to improve the permeability and mechanical strength level of the refractories at different temperatures. The collected results attested that the selected additives were more efficient in optimizing the drying behavior of the CAC-bonded compositions, whereas the HA-containing castables performed better when the aluminum-based salt was blended with a small amount of CAC (0.5 wt%), which changed the binders hydration reaction sequence and optimized the permeability level of the resulting microstructure. Consequently, some of the designed compositions evaluated in this work showed improved drying behavior and no explosion was observed even during the tests carried out under a high heating rate (20 °C/min).     

Use of Ozone for Gold Extraction from a Highly Refractory Concentrate

Precious metals are generally recovered from their ores by cyanide leaching. When the gold or silver are locked up in the mineral matrix, they remain unrecovered and the ore is classified as refractory to cyanidation. Ozonization in acidic media of an arsenopyritic-pyritic highly refractory gold concentrate (110 g Au/t) as a treatment prior to cyanidation was evaluated. While the conventional cyanidation of this concentrate recovers only 9% of the gold, a pretreatment with ozone before the cyanidation increases the gold recovery to 23%. The rest of the gold is in solid solution with the matrix. Even if this increase in gold extraction is not large enough to economically process this specific concentrate, it demonstrates that the gold locked up in pyrite or arsenopyrite could be recovered by ozonating the ore before cyanidation.     

Shaped Insulating Refractory ProductsFireclay Bricks

正1 Scope This standard specifies the classification,shape and dimensions,technical requirements,test methods,quality appraisal procedures,packing,marking,transportation,storage,and quality certificate of fireclay insulating refractory bricks.This standard is applicable to fireclay insulating refractory bricks used for insulating layer and furnace lining not contacting with high temperature melt and corrosive gas.     

化学氧化强化湿法冶金清洁生产：进展与展望

湿法冶金具有能耗低、污染小等优点，广泛应用于低品位复杂矿石处理。金属浸出是湿法冶金的首要环节，但存在金属回收率低和反应时间长等问题。化学氧化可加速金属硫化物转化为金属离子或改变金属的价态，有利于后续目标金属的分离富集，在此过程中还可以通过介质强化、外场强化提高金属氧化浸出率。主要介绍了五种典型的低腐蚀性化学氧化剂(Fe3+, O2, H2O2, O3和过硫酸盐)，以及相关的协同氧化方法在金属浸出中的应用和机理分析，介绍了加压强化、介质强化、微波和超声等强化方法，对比分析了各方法的优缺点及适用范围。Fe3+广泛应用于硫化矿的酸性浸出，独特的离子对循环使Fe3+可与多种氧化剂形成协同氧化浸出机制。O2常通过加压强化提升氧化浸出效率，可促进难处理硫化矿氧化分解。H2O2氧化性强，氧化产物清洁无污染，受到广泛关注，近年来多用于电子废弃物资源处理领域。臭氧预氧化处理含硫含砷难处理金精矿，可有效解除难浸硫化矿对金的包裹，促进金的溶出。过硫酸盐性质稳定，氧化能力强，可活化生成更高氧化性的活性氧。协同氧化可结合各氧化剂的优点，提高氧化能力，降低综合成本。四种强化方法可为化学氧化过程提供能量、加强传质或提高金属分离选择性，有助于提高金属浸出率，缩短反应时间。展望了化学氧化强化金属浸出技术的发展前景和技术挑战，对湿法冶金清洁生产技术开发有指导意义。     

Refractory metal silicides reinforced by in-situ formed Nb2O5 fibers and mullite nanoclusters

There is keen interest in the use of refractory metal silicides as structural materials or thermal barrier coatings for a high temperature environment. However, a long-standing problem for these materials is their poor thermal shock property. To address this challenge, Nb-Al-SiC elements were introduced into the MoSi₂ matrix and consolidated by in-situ hot pressing. We find that this treatment leads to improved performance of MoSi₂ composites in high temperature thermal shock resistance and bending strength. After in-situ HPing, the Nb, Al₂O₃ particles, and SiC nanoclusters were uniformly dispersed in the MoSi₂ matrix and inhibited the movement of dislocation, resulting in a strengthening effect. During the thermal shock process, the fragmentized oxide layer present in the surface of the pure MoSi₂ alloy disappeared completely, and a dense multi-component oxide layer was formed in-situ on the surface of the MoSi₂ composites. The dense multi-component oxide layer was composed of SiO₂ glass, fiber-structured Nb₂O₅, and nano-sized mullite phases. The fiber structured and nano-sized oxide phases play an important role in strengthening the oxide layer.     

Investigation of the refractory bricks used for the flue wall of the horizontal anode baking ring furnace

Anode manufacturing, particularly the baking process, is an important part of the primary aluminium production process. Anode baking is carried out in closed or open top ring furnaces. The anodes are placed in pits and surrounded by packing coke to prevent oxidation by infiltrated air and mechanical support. The anodes are baked through indirect contact with the hot gas flowing in the flues on both sides of the pit. The flue walls are made of commercial refractory bricks, which are subjected to chemical (high temperature corrosion), mechanical (creep, walls, anode loading and unloading) and thermal (high temperature, thermal shock) conditions during the baking process. The resulting stress causes chemical and physical alterations across the width of the wall. This stress generally manifests in the collapsing, cracking and bending of flue walls. The chemical composition and physical properties of refractory bricks taken from degraded flue walls in an industrial plant were investigated, and it was shown that regular redressing and maintenance of flue walls can prevent or reduce additional energy consumption due to pit deformation, consequently reducing the cost of anode production.     

The Role of Refractory Metal Additions in Precipitation Processes in Superalloys

Superalloys are multi-component alloys containing many alloying additions developed for high temperature applications. Refractory metals are added to impart beneficial properties to the alloy. The role refractory metal additions in precipitation processes in superalloys are discussed in this paper. The minor variation in the alloying additions on the changes in precipitation behaviour are illustrated with the example of Alloy 718 and Alloy 625.     

The Role of Refractory Metal Additions in Precipitation Processes in Superalloys

Abstract

Superaltoys are multi-component alloys containing many alloying additions developed for high temperature applications. Refractory metals are added to impart beneficial properties to the alloy. The role refractory metal additions in precipitation processes in superalloys are discussed in this paper. The minor variation in the alloying additions on the changes in precipitation behaviour are illustrated with the example of Alloy 718 and Alloy 625.     

Flotation technology of refractory low-grade molybdenum ore

Because of the low grade, high oxidation rate and the accumulation of little associated metal sulfide ore in the molybdenum concentrate during flotation, the Qingyang molybdenum ore is difficult to beneficiate. The experimental studies of grinding fineness, the amount of roughing modifier, depressant and collector were completed. In the cleaning process, the contrast experiments of one regrinding, the regrinding and scrubbing, two-stage regrinding was carried. The result shows that the grade of molybdenum ore concentrate is 45.31%, the recovery is 65.98% and the rich ore ratio reaches 20.59% by the regrinding and scrubbing seven cleaning, the regrinding of concentrations from middling of molybdenum-sulfur separation. The regularly-concentrated material from the apparatus was as the middling products. Hence, ideal beneficiation index can be obtained with a rational mineral processing, which offers new beneficiating technology for the refractory low-grade molybdenum ore in China.     

Corrosion of nickel ferrite refractory by Na3AlF6–AlF3–CaF2–Al2O3 bath

Based on research on cermet inert anodes for aluminium production, it has been suggested that nickel ferrite spinel might be suitable for use as a sidewall refractory in Hall-Héroult cells. A corrosion resistant sidewall would allow elimination of the frozen bath ledge, and has potentially huge benefits in terms of energy savings and increased productivity. However, little work has been done to assess nickel ferrite's suitability as a refractory.Dense nickel ferrite samples were prepared and characterized, and corrosion tests in cryolite based baths were conducted. Results confirm that the spinel does have good corrosion resistance. The corrosion mechanism is complex, involving grain boundary attack and formation of a Ni–Fe alloy. This alloy could pose a risk in terms of contamination of the aluminium. The use of additives to restrict penetration of grain boundaries may be the key to development of a successful spinel based refractory.