There are a number of other routes for producing alumina that have been practiced or investigated over the decades, however none of these have been viable outside controlled economies of the past. Alumina containing inputs to these processes can include bauxite, but are more typically other lower cost materials such a aluminous clays, high alumina fly ash, or in the case of a former Soviet plant, nepheline.
Very often these non-Bayer processes would rely on the sales of by-products such as cement or zeolites to be economic.
Processing bauxites or other alumina containing minerals with acids has been experimented with extensively. No large scale commercial plants have ever been constructed due to higher operating and capital costs. Additionally corrosion problems and potential leaks of toxic reagents (eg chlorine gas) add to potential operating difficulties. The acid routes, due to their ability to produce a very high purity alumina in a single process, do have potential for the production of small quantities of high purity alumina for specialised applications (but not SGA).
The Greymeck process once operated in Poland is essentially a wet cement process that also produces alumina; it produces around 9 tonnes of cement for every tonne of alumina. Based around sinter technology, one plant in China (Mengxi) has been built around this technology. The aluminous feed stock for the process is high alumina fly ash.