Four-step eco-friendly energy efficient recycling of contaminated Nd2Fe14B sludge and coercivity enhancement by reducing oxygen content

Complete recycling of Nd2Fe14B sludge by chemical methods has gained significance in recent years, however, it is not easy to recycle highly contaminant sludge and obtain product with good magnetic properties. Herein we report a simple four-step process to recycle the Nd2Fe14B sludge containing ~ 10% of contaminants. Sludge was leached in H2SO4 and selectively co-precipitated in two steps. In the first co-precipitation, Al3+ and Cu2+ were removed at pH 6. Thereafter, in the second co-precipitation Fe2+ and RE3+ sulfates were converted to the Fe and RE hydroxides. By annealing at 800 °C RE and Fe hydroxides precipitates were converted to the oxides and residual carbon was oxidized to CO2. After the addition of boric acid, Fe and RE oxides were reduced and diffused to the (Nd-RE)2Fe14B by calciothermic reduction diffusion. Removal of CaO by washing with D.I. water in glove box reduced the oxygen content (~ 0.7%), improved crystallinity and enhanced the magnetic properties significantly. Coercivity increased more than three times (from 242.71 to 800.55 kA/m) and Mr value was also enhanced up to more than 20% (from 0.481 to 0.605 T). In this green process Na2SO4 and Ca(OH)2 were produced as by-product those are non-hazardous and were removed conveniently.

Calciothermic powders of rare metals and intermetallic compounds

This paper presents a profound review of scientific and technical literature on the issues of calciothermic production of powders of rare metals, intermetallic compounds, composite materials and refractory oxygen-free compounds (carbides, nitrides). Calciothermic reduction is a metallothermic synthesis method for those substances where calcium or its derivatives, such as calcium hydride or calcium carbide, are used as a reducing agent. Thermodynamics aspects of a reduction process are covered in the paper broadly, with particular emphasis on assessing the reduction depth of original oxide raw materials, as TiO2. The mechanism and kinetics of calciothermic synthesis of single-component and multi-component alloys are described. Presented are both technological means of obtaining materials and hardware resources of many varieties of calciothermic method. The key features of the work are generalization and systematization of properties (chemical, physical, technological) of materials synthesized by calciothermic method. The data are accumulated in the appropriate tables and divided by substance classes (powders of metals and alloys, powders of intermetallic compounds, powders of carbides, powders of nitrides, and powders of composite materials). Methods of calciothermic powder making in case of the singlecomponent and complex multi-component systems are briefly described. This work will be interesting to the students of metallurgical profile and specialists whose scientific interests are in the field of material synthesis by methods of powder metallurgy.

Titanium Production via Titanium Sulfide

A new metallurgical process via titanium sulfide from ilmenite is proposed and experimentally approved: It consists of several stages; 1) The ilmenite ore is exposed to gaseous CS2 to selectively sulfurize to FeS, which is wet-chemically removed. 2) The residual oxide is again exposed to CS2 to form TiS2. 3) TiS2 is electrochemically reduced to metallic Ti using molten CaCl2-CaS as an application of OS process. TiFeO3 was exposed to Ar-CS2 mixed gas flow at 1173 K to form the mixture of FeS+TiO2. FeS was easily separated by immersing in H2SO4 solution at 313 K. After recovery of TiO2, it was converted completely to TiS2 by the second sulfurization with CS2. TiS2 could be reduced to Ti powder by calciothermic reduction and simulteneous electrolysis in a CaS-CaCl2 melt for about 6 hours at 1173 K and 3.0 V. The impurity decreased to a low level such as 0.021 mass%S due to very small solubility of S in a-Ti. However, 1.06 mass%O remained because of wide solubility of oxygen in a-Ti and water contamination in initial CaCl2.