Soyaux was initially a horticulturalist and then studied botany in
Berlin. The
Deutsche Afrika Gesellschaft (German Africa Society) funded him as a botanist on the expedition of
Paul Güssfeldt to the
Kingdom of Loango. On the expedition, Soyaux traveled at the end of 1873 to the Loangoan coast in what is now
Cabinda Province, where he joined Güssfeldt, Julius Falkenstein and
Eduard Pechuël-Loesche. In 1875 Soyaux was commissioned to go to Angola, where he met
Paul Pogge. Soyaux returned in mid-1876 to Germany. In the years from 1876 to 1879 he published
Der verlorene Weltteil (Berlin, 1876) and
Aus Westafrika (2 vols., Leipzig, 1879).
F. A. Brockhaus AG published Soyaux's "Deutsche Arbeit in Afrika: Erfahrungen und Betrachtungen" (Leipzig, 1888). In the spring of 1888 Soyaux went to Brazil on behalf of the
Siedlungsgesellschaft Herman, a colonial land-developing company. He led the colony Bom Retiro in the province
Rio Grande do Sul. In 1904 he was one of the founders of the
Centro Econômico do Rio Grande do Sul. He then lived in
Porto Alegre. ==Selected publications==