Alkaline pressure leaching

APOL [Alkaline pressure oxidation leaching] A process for extracting gold from refractory ores, developed by Davy McKee (Stockton, UK). 

Plastic components can be leached into the product and the alkalinity also can be affected by certain types of glass (qv). Particulate matter can be introduced by flaking from container surfaces. The containers also must be able to withstand the heat and pressure of sterilization. 

It has already been mentioned that one of most used forms of Ni is Raney Ni which is obtained from Ni-Al or Ni-Zn alloys by leaching A1 or Zn in alkaline solution. However, the properties of the resulting electrocatalyst appear to depend on the nature of the precursor [135], Methods of application of the alloys are various [135]. A particularly convenient one is the so-called LPPS (low pressure plasma spray) [146]. Raney Ni prepared in this way has shown that lower Ihfel slopes can be obtained, thus suggesting a real electrocatalytic effect (Fig. 11). On such highly porous Ni it is possible that the proportion of particularly active sites (at the edges and peaks of crystallites [262] increases considerably. However, the effect of temperature on the Tafel slope is more than anomalous [248] suggesting indeed some temperature-induced surface modifications. In fact, recrystallization phenomena are observed which can be minimized by means of small additions of Ti, Mo or Zr. The... 

For the first step, 12 g. of ground coal and 120 ml. of alkaline solution were mixed and placed in a 300-ml. stainless steel autoclave equipped with a turbine agitator. The system was flushed with nitrogen and then heated to the desired temperature while the mixture was stirred continuously. After a period of treatment at constant temperature and pressure, the autoclave was cooled quickly, and the contents were filtered to recover the coal. The filter cake was washed with 400 ml. of distilled water, dried at 90 C for 4 hr., weighed, and analyzed for total sulfur and ash. A portion of the alkali-treated coal (usually 2.5-3.0 g) was leached for an additional... 

The uranium(IV) is first oxidized in the alkaline medium by ambient oxygen to uranium(VI). Leaching with alkali under pressure has been carried out for a long time. 

Previous work has shown that ash-forming mineral matter, including iron pyrites, can be removed from coal by leaching the finely divided material with a hot caustic solution under pressure followed by washing with a dilute mineral acid (1-6). Recently, similar results have been achieved in leaching fine-size coal with hot sodium carbonate solutions (J7). In both cases, quartz appears to dissolve in the hot alkaline solution, while clay minerals and iron pyrite are converted into acid-soluble compounds which are removed in the acid washing step. Acid also removes any carbonate minerals which are present in the coal. 

However, as a result of growing concerns regarding leaching of arsenic salt around the home and in children s play areas, the Environmental Protection Agency (EPA) announced on February 12,2002 a voluntary decision by the industry to move away from the consumer use of CCA-treated lumber by December 31,2003, in favor of new alternative wood preservatives. According to the EPA, these alternatives of CCA are alkaline copper quarternary (ACQ), copper boron azole (CBA), cyprocon-azole, and propioconazole. Besides, as an alternative to pressure-treated wood, EPA has suggested to use WPC materials. 

Pulverized coal is leached with alkaline solution of Na2C03 containing dissolved oxygen or air under pressure at temp of about 150 C. Oxygen partial pressure 1.34 MPa. Residence time 1 hr. 

China s Yichun Li—Ta—Nb mine in 1998 accounted for 90% of the country s recoverable hthium reserves, and its lepidolite was easily obtained as concentrates from the open pit mine s tantalum and niobium processing. However, initially there was only a small amount of lithium carbonate processed from this ore due to the high cost of the lime sintering process (see the American Potash and Chemical Co. Section, above). To reduce these costs a pressurized ammonium chloride leach process has been suggested by Xu et al. (1998). In this process lepidolite concentrates (Table 1.18) would be initially partially defluorinated by being heated to 850°C for 20 min, and then ground to a —74 pm ( 200 mesh) size. The roasted concentrates would be cooled and made into a 25% aqueous slurry, with 3.5 mol of ammonium chloride being present per mole of total alkaline solids in the concentrate. The slurry would be heated under pressure at 240°C for 90 min, and then cooled, filtered and washed. The process was estimated to leach about 95% of the lithium, but the filtrate would also contain most of the other alkali metals in the ore. The filtrate would consequently be evaporated to crystallize the sodium, potassium. 

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