Nowadays, sustainability and good use of resources and waste are necessary. So, this work seeks to synthesize a ceramic material from natural waste, as well as its characterization and biological evaluation after all the steps that anticipate in vivo application. In this way, brushite, which is a dihydrate dicalcium phosphate mineral that is a calcium phosphate present in the natural mineralization of tissues, can be obtained synthetically from chicken eggshells. It is used as a biomaterial for different applications such as medical treatment, especially orthopedic treatment and bone repair, agrobiological inorganic fertilizers. Brushite has the property of adsorbing ions and changing its active sites with calcium, such as Zn and Ag ions, which can enhance the biocompatible and bactericidal potential of the biomaterial, respectively. In this work, we started with the synthesis of bruxite nanopowders (previously performed) that was characterization by microscopy and physical-chemistry analysis (MEV-topography, MET-nanoscale, FTIR-chemistry-group, XRD Rietveld- material identity). The cytotoxicity was then tested by in vitro microbiological analysis in a nutrient medium using 3 species of bacteria was made ISO-10993-5- ceramic tests. The results shows that was possible to obtain bruxite through the results of chemical-physical characterization and the initial results in vitro indicate that it is a biocompatible nanoceramic. 

Thanks to Faperj 203.409/2023 - SEl-260003/016585/2023 for supporting the research, to CAPES, CNPQ and to the student Ronald Palandi Cardoso for helping with the cultivation of microorganisms and to Prof. Yutao Xing for helping with the MET analysis.

The present situation of the market and applications of rare-earths is reviewed. It is given special attention for discussing the possibility of substitution of  rare-earth magnets by other families of magnets.

Three are the main commercial applications of rare-earths: i) luminescent phosphors, ii) magnets, and iii) catalysis.

For catalysis, the cheap rare-earths as cerium and lanthanum are employed.  Luminescent phosphors are essential in many applications, as lasers and, for example, erbium is used in optical fibers. However, in spite of its relevance, erbium is not expensive as Tb and Dy. 

In LED applications, the rare-earths are used as thin films, and , thus the demand in volume  is not very significant when compared with the demand for magnets. The use of white LED (light emission diode) significantly reduced the demand for europium after 2015, but this application is still relevant. In the 1960s and up the 1980s, Europium was the most expensive rare-earth, due to extreme demand.

The rare-earth market is nowadays driven by Tb, Dy, Nd and Pr, which are employed in rare-earth iron permanent magnets of the RE2Fe14B family (RE=rare earth). For applications in high temperature, dysprosium and terbium are added, and this made the demand and price of Dy and Tb be skyrocketing.

SmCo magnets have the problem of using the expensive element cobalt. Nowadays the demand and price of cobalt increased conbseiderably due to application in rechargeable battteries, and thus, SmCo use in large scale is avoided, but they remain relevant for high temperature applications (above 150oC).

Possible alternatives for rare-earth  permanents magnets are discussed. Among the few options for replacement are the ferrite magnets (BaFe12O19 or SrFe12O19), the Alnico magnes based on shape anisotropy and maybe iron nitrogen. Economic and technical feasibility of these families of magnets are discussed.

Its is given a brief overview about recent mining projects in Brazil, which are focusing on ionic clays, with the objective of extracting the scarce and expensive elements terbium and dysprosium. 

It was recently presented a model [1-3] able to predict the magnetic anisotropy of any sample, This is called the "Simultanoeus Fitting Method" SFM.

According the SFM method, the magnetic anisotropy can be determined, since magnetic measurements are performed at the  (_|_) perpendicular and (//) parallel directions (relative to the alignment direction). The method assumes samples with alignment in one preferential direction, thus with uniaxial anisotropy. This kind of anisotropy is typically found in samples prepared by powder metallurgy, where the alignbment is obtained by applying magnetic fields in grains with single domain size. 

Using the SFM, the crystallographic texture of samples can be determined directly from magnetic measurements, avoiding complicated, laborious and expensive techniques as EBSD - Electron BackSacterred Diffraction.

A symmetrical distribution as for example the Gaussian, is used for describing the crystallographic texture.

Other distribution functions can also be used, since they are symmetrical. This includes Cauchy -Lorentz, Voigt and Pearson VII as possibilities.

It is experimentally found that f=cos(theta)^n or Gaussian distributions describe very well the texture of the samples.

The model allows the re-evaluation of experimental data. Here it is discussed how to apply the model in very different samples.

These samples are SmFeN (magnetocrystalline anisotropy), Alnico, (shape anisotropy [4,5]) and cobalt-needle samples.

In cobalt needle samples the shape anisotropy and the magnetocrystalline anisotropy may have the same order of magnitude.

It is discussed the question of dominant anisotropy.