  In this work we study a r-species mixture of gases within the relativistic
kinetic theory point of view. We use the relativistic covariant full Boltzmann
equation and we incorporate the Schwarzschild metric. The method of solution of
the Boltzmann equation is a combination of the Chapman-Enskog and Grad
representations. The thermodynamic fluxes are expressed as functions of the
thermodynamic forces so that the generalized expressions for the Navier-Stokes,
Fick and Fourier laws are obtained. The constitutive equations for the
diffusion and heat fluxes of the mixture are functions of thermal and diffusion
forces which depend on the acceleration and the gravitational potential
gradient. While this dependence is of relativistic nature for the thermal
force, this is not the case for the diffusion forces. We show also that the
matrix of the diffusion coefficients is symmetric and the thermal-diffusion
coefficient is equal to the diffusion-thermal one, proving the Onsager
reciprocity relations. The entropy flux of the mixture is also expressed in
terms of the thermal and diffusion forces, so that its dependence on the
acceleration and gravitational potential gradient is also determined.
