  We present ALMA band 6 observations of the luminous blue variable Eta Car,
obtained within the ALMAGAL program. We report SiO J=5-4, SiS J=12-11 and SiN
N=5-4 emission in the equatorial region of the Homunculus nebula, constituting
the first detection of silicon- and sulphur-bearing molecules in the outskirts
of a highly evolved, early-type massive star. SiO, SiS and SiN trace a clumpy
equatorial ring that surrounds the central binary at a projected distance of 2
arcsec, delineating the inner rims of the butterfly-shaped dusty region. The
formation of silicon-bearing compounds is presumably related to the continuous
recycling of dust due to the variable wind regime of Eta Car, that destroys
grains and releases silicon back to gas phase. We discuss possible formation
routes for the observed species, contextualizing them within the current
molecular inventory of Eta Car. We find that the SiO and SiS fractional
abundances in localised clumps of the ring, $6.7\times10^{-9}$ and
$1.2\times10^{-8}$ respectively, are exceptionally lower than those measured in
C- and O-rich AGB stars and cool supergiants; while the higher SiN abundance,
$3.6\times10^{-8}$, evidences the nitrogen-rich chemistry of the ejecta. These
abundances must be regarded as strict upper limits, since the distribution of
H2 in the Homunculus is unknown. In any case, these findings shed new light
onto the peculiar molecular ecosystem of Eta Car, and establish its
surroundings as a new laboratory to investigate the lifecycle of silicate dust
in extreme astrophysical conditions.
