The invention provides a method of manufacturing a magnesium sulphate product, and a crystalline product comprising magnesium sulphate in the form of crystal or granules. The method comprises the steps of: providing a sulphuric acid product that has been obtained as a by-product during the sulphate process for manufacturing titanium dioxide; concentrating the sulphuric acid product to obtain a concentrated product that has a higher sulphuric acid concentration; combining a magnesium-based neutralising agent with the concentrated product and allowing the magnesium-based neutralising agent and the sulphuric acid to react, to generate magnesium sulphate in solution; and crystallising magnesium sulphate out of the solution, to obtain a crystalline magnesium sulphate product together with a remaining liquor. The crystalline magnesium sulfate may be mixed with an agriculturally acceptable carrier of diluent and/or with other fertiliser materials to produce a fertilizer.