Abstract: The invention concerns a method for preparing organic waste, such as coffee grounds (12), so as to eliminate it by combustion. Said method consists in mixing the waste (12) with a silicic acid additive (14), the proportion of additive ranging between 3 and 5% to constitute a fuel.

Abstract: A method for purifying sludge suspected of containing heavy, toxic and/or precious metals in order to extract them, the sludge being suspended in an aqueous solution and together forming a mass to be treated. FeCl3 is mixed with the mass, until an acidic pH of the solution is obtained. (CO2H)2 and NH4Cl are then mixed with the mass until metal pro-chelates are formed. Mixed alkali sulfides are then mixed with the mass until a solution with a very basic pH is obtained, to form colloidal complex iron chelates, which trap the metals. The solution is neutralized by adding an acid, until alkaline-ferrous sulfides and hydroxides containing the metals are precipitated. The mass is then centrifuged to form from the mass a liquid phase and a solid phase, the solid phase containing the alkaline-ferrous sulfides.