Results of the studies on surface cleaning of the end-of-life R-Fe-B (R = Nd, Pr, Tb, Dy) system magnets by chemical etching to involve them in recycling are presented. The material for experiments included magnets that were disassembled from the end-of-life hard disk drives for personal computers. The choice of these parts was conditioned by their low cost, easy disassembling, and small size. Disassembled magnets were demagnetized at 623 K and medium vacuum through 4 h. Sandblasting with slag abrasives supplied at a pressure of 300 kPa was carried out to remove the electrodeposit coating from their surface. A specimen was prepared on the cleaned surface, which was subjected to oxidation under natural conditions. The effect of acid type (nitric, hydrochloric, sulphuric) and acid solution concentration on the efficiency of etching the oxidised surface and on the behaviour of rare-earth and doping elements during chemical etching was investigated. The morphology of specimen surface and oxygen content were analysed by scanning electron microscopy. It has been found that chemical etching with 0.5-1.0 wt% sulphuric acid solution for 1 min leads to a decrease in oxygen content from 3.1±0.2 to (2.2±0.2)-(2.4±0.1) wt% on the surface of the major stoichiometric phase of the alloy, as well as to etching the phases enriched with rare-earth metals off the surface and to the formation of pores on their place.
Grachev et al. (Fri,) studied this question.