a process is provided for making thermoplastic - composites from recycled thermoplastics together with phosphogypsum waste by - product from the phosphate fertilizer wet process or , in an equally preferred embodiment with fluorogypsum waste by - product from fluorine production wet process to produce lumber profiles . the process involves admixing phosphogypsum and / or fluorogypsum waste byproduct and / or flue gas desulfurization gypsum and / or crude gypsum and / or calcined gypsum with thermoplastics and a functionalized compound with or without coupling agents to produce a filled thermoplastic - composite composition , and melt processing the composition to produce a filled thermoplastic - composite article . the articles are preferably in the form of railroad cross ties or construction articles such as common lumber profiles , panels , tiles , poles , utility poles , crossarms for utility poles , roofing tiles , pipeline skids , pilings , marine fender - piles , bulkheads , revetments , and are useful for constructing various structures , such as oilfield board roads and equipment mats . the process avoids the accumulation of undesired phosphogypsum / fluorogypsum “ stacks ” and provides environmentally friendly useful products which require no chemical preservatives to prevent insect infestation or decay from the elements . tailings from ore processing can also be used as a filler .