摘要:
The invention relates to a silicon-containing substrate coated with one or more layers, at least one of which contains or is made of calcium phosphate (Ca3(PO4)2), calcium arsenate (Ca3(AsO4)2), mixed calcium phosphate-calcium arsenate layer or the corresponding hydrates, as well as to the production and use of said substrate.
摘要:
The invention relates to a method for precipitating pentavalent calcium arsenate from an acidic solution, in which arsenic is at least partially in trivalent form. The acidic solution is neutralised before being routed to an arsenic oxidation stage,and a poorly soluble calcium-arsenic compound is precipitated from the solution, in which all the arsenic is pentavalent.
摘要:
Methods for waste treatment and compositions of stabilized waste elements are provided, typically for the disposal of arsenical wastes. Arsenic trioxide waste produced as a by-product of metal extraction is slurried in water for from 6 to 24 hours with finely divided quicklime to produce nonvolatile calcium arsenate (III). An excess of CaO stoichiometry with As is used to consume secondary waste species such as sulphate, silicate and iron oxides. The precipitated arsenate is oven dried at 120 °C and then calcined in air between 15 minutes to several hours at 1000 °C to 500 °C respectively to oxidize arsenate (III) to arsenate (V) as Ca5(AsO4)3(OH) (an apatite) as the major arsenic immobilization phase, with minor arsenic incorporated in Ca3(AsO4)2. Calcium sulphate anhydrate (sulphate immobilization) and calcium iron oxide (iron immobilization) are also produced. Tertiary immobilization is achieved milling or fracturing and incorporating the apatite an encapsulant consisting of ordinary portland cement and flyash. After curing for one month in steel drums in a water saturated atmosphere, the waste form is ready to be transported either to a repository or to be used as landfill. Further security may be achieved at the back end of the process by lining the repository with ferric clays that will strongly absorb and adsorb heavy metal species which may escape.
摘要:
PCT No. PCT/AU93/00489 Sec. 371 Date May 1, 1995 Sec. 102(e) Date May 1, 1995 PCT Filed Sep. 21, 1993 PCT Pub. No. WO94/06575 PCT Pub. Date Mar. 31, 1995Methods for waste treatment and compositions of stabilized waste elements are provided, typically for the disposal of arsenical wastes. Arsenic trioxide waste produced as a by-product of metal extraction is slurried in water for from 6 to 24 hours with finely divided quicklime to produce nonvolatile calcium arsenate (III). An excess of CaO stoichiometry with As is used to consume secondary waste species such as sulphate, silicate and iron oxides. The precipitated arsenate is oven dried at 120 DEG C. and then calcined in air between 15 minutes to several hours at 1000 DEG C. to 500 DEG C. respectively to oxidize arsenate (III) to arsenate (V) as Ca5(AsO4)3(OH) (an apatite) as the major arsenic immobilization phase, with minor arsenic incorporated in Ca3(AsO4)2. Calcium sulphate anhydrate (sulphate immobilization) and calcium iron oxide (iron immobilization) are also produced. Tertiary immobilization is achieved milling or fracturing and incorporating the apatite an encapsulant consisting of ordinary portland cement and flyash. After curing for one month in steel drums in a water saturated atmosphere, the waste form is ready to be transported either to a repository or to used as landfill. Further security may be achieved at the back end of the process by lining the repository with ferric clays that will strongly absorb and adsorb heavy metal species which may escape.
摘要:
This invention provides a process for the conversion of hazardous hexafluoroarsenic acid or a salt thereof to an arsenate salt that can be rendered non-hazardous. In particular, hexafluoroarsenic acid or a salt thereof is converted to the solid insoluble calcium or magnesium arsenates or mixtures thereof which are water insoluble. Known stabilization technology renders the material non-hazardous. The present process involves converting hexafluoroarsenic acid or a salt thereof contained in an aqueous mixture to an insoluble arsenate salt. The process comprises the steps of: (a) adding a first compound selected from group (I) or group (II) to the aqueous mixture in an amount sufficient to substantially neutralize the aqueous mixture to a pH greater than or equal to about 10; and, if the first compound is selected from group (II), in an amount sufficient to substantially convert fluoride ions to solid water insoluble calcium or magnesium fluorides or mixtures thereof and to substantially hydrolyze the hexafluoroarsenic acid or salts thereof to solid water insoluble calcium or magnesium arsenates or mixtures thereof in subsequent step (b), and if the first compound is selected from group (I), adding a second compound from group (II) in an amount sufficient for said conversion of fluoride ions and said hydrolysis; and (b) reacting the mixture resulting from step (a) at a temperature and for a time sufficient for said conversion of fluoride ions and said hydrolysis. Prior to said step (a), the process further has the benefit of recovering the hydrogen fluoride from the starting aqueous mixture as a product if desired or for decreasing the volume of waste to be rendered non-hazardous.
摘要:
This invention provides a process for the conversion of hazardous hexafluoroarsenic acid or a salt thereof to an arsenate salt that can be rendered non-hazardous. In particular, hexafluoroarsenic acid or a salt thereof is converted to the solid insoluble calcium or magnesium arsenates or mixtures thereof which are water insoluble. Known stabilization technology renders the material non-hazardous. The present process involves converting hexafluoroarsenic acid or a salt thereof contained in an aqueous mixture to an insoluble arsenate salt. The process comprises the steps of: (a) adding a first compound selected from group (I) or group (II) to the aqueous mixture in an amount sufficient to substantially neutralize the aqueous mixture to a pH greater than or equal to about 10; and, if the first compound is selected from group (II), in an amount sufficient to substantially convert fluoride ions to solid water insoluble calcium or magnesium fluorides or mixtures thereof and to substantially hydrolyze the hexafluoroarsenic acid or salts thereof to solid water insoluble calcium or magnesium arsenates or mixtures thereof in subsequent step (b), and if the first compound is selected from group (I), adding a second compound from group (II) in an amount sufficient for said conversion of fluoride ions and said hydrolysis; and (b) reacting the mixture resulting from step (a) at a temperature and for a time sufficient for said conversion of fluoride ions and said hydrolysis. Prior to said step (a), the process further has the benefit of recovering the hydrogen fluoride from the starting aqueous mixture as a product if desired or for decreasing the volume of waste to be rendered non-hazardous.