I do very little use of the talcum for pleurodesis and justly one the problems, specially for we, is to be sure that is free of asbestoss and by other side requires careful special for the esterilizacion . I have found . a work that mentions what your ask. The work is "Thoracoscopy and Talc Poudrage for Pneumothoraces and Effusions " ..." the talc used was US Pharmacopeia talc , a hydrous magnesium silicate known in its native form as soapstone or French chalk. The talc was especified by the manufacturer ( Humco Laboratory , Texar-kana , TX ) to be free from asbestos . I Expect that these reference will be usefull to You and if could get it in U.S.A. wold be important to know as has at it done given that is a problem for all of Us to get that famous talc .