摘要:
The chromic anhydride contained in soluble form (chromic acid) in exhausted, polluted chromium plating baths is recovered by alkalizing the exhausted chromium plating liquid to a pH comprised between 3 and 7 at a temperature of 70°C with a commercial sodium hydroxide solution, keeping the mass in reaction at this temperature for an hour and filtration separating the precipitate obtained. The filtered solution having a specific gravity of 1.25 kg/l, contains CrO3 (22 % in weight) which is then reduced with sulphur dioxide to obtain a solution containing basic chromium sulphate and sodium sulphate, suitable for use as a tanning bath; in this manner pollution is avoided and the waste chromium is exploited. The solution containing CrO3 can also be introduced into a hexavalent chromium salt production cycle.
摘要:
In the electrochemical regeneration of chromic-sulphuric acid, the sulphuric acid chromium-III-sulphate solution is fed into the electrolysis cells under pressure. This reduces production breakdowns. Fluctuations in the flow available can be flexibly handled. The chromium-sulphuric acid is produced in uniform quality.
摘要:
A re-calcination and extraction process for the detoxification and comprehensive utilization of chromic residues, comprising adding small amount of residue ore powder, sodium carbonate, or additionally, a certain amount of coke powder to the poisonous chromic residues, and calcining the mixture in a re-calcinating apparatus at 1000-1200°C, for 30-60 minutes. The re-calcined grog is extracted with water, to obtain an extractive liquor containing sodium chromate. The extractive liquor can be used to produce chromium oxide, basic chromium sulfate or medium chrome yellow; while the extracted residues can be sintered at high temperatures with iron ore powder and coke to obtain a massive self-melting sintered iron, which can be further converted to a low-chromium cast iron. This process can thoroughly detoxify the chromic residues, effectively recover Cr2O3 and remove water-soluble Cr+6, whereby various important industrial materials are produced. The method brings very good economical and environmental benefits.
摘要:
L'invention se rapporte à un sulfate ferreux heptahydraté technique traité pour éliminer des traces d'eau intercristalline contenant de l'acide libre et ainsi le rendre susceptible d'écoulement libre. Le traitement consiste à le mélanger avec des phosphates calciques anhydres broyées finement, contenant au moins un atome de calcium pour un atome de phosphore. Au contact de l'acide sulfurique, il se forme à partir d'orthophosphates tri ou bicalciques, ou leur précurseur pyrophosphate et métaphosphate, des orthophosphates bi ou monocalci- ques, qui cristallisent avec de l'eau de substitution. A partir d'un sulfate ferreux brut, qui s'agglomère en masses, on obtient des produits parfaitement fluides contenant de 90 à 97 % de cristaux de sulfate de fer heptahydraté, et d'aspect très voisin du sulfate ferreux heptahydraté. On peut associer ce traitement à un traitement classique, tel que mélange avec un sulfate ferreux partiellement déshydraté et un neutralisant tel que carbonate de calcium. Par ailleurs le procédé est applicable à d'autres sulfates métalliques hydratés cristallisés, sulfate cuivrique, sulfates d'aluminium, de magnésium et de zinc.