Alkaline leaching effectiveness

Alkaline solutions effect on wood, 26 352 in leaching chemistry, 16 152 sodium nitrite in, 22 853-854 Alkaline sulfite pulping, 21 22, 25 Alkalinity... 

To determine the effect of the final temperature during the alkaline leaching of Cherokee coal, several runs were carried out in which different portions of the coal were treated with 1.0 M Na2C03 for 1.0 hr. at various final temperatures. The alkali-treaTed coaT was then leached with HN03. The results of the alkaline leaching step are indicated in Figure 3 and the overall results in Figure 4. 

Effect of test water alkalinity. The effect of alkalinity appears obvious for all materials when comparing results for soft migration water (20 ppm CaCOs) and medium mineralized migration water (200 ppm CaCOs). pH increase and aluminium leaching were far more significant with soft water than with medium mineralized water. Caleium eoneentration alw s increased (calcium migration from the cement) in soft waters (initial Ca = 8 mg/1) but it decreased or remained unchanged in medium mineralized water (preeipitation of CaCOs or equilibrium). 

Figure 7.9 shows the activity for H2 evolution of three samples of Ni [27]. Smooth and sandblasted Ni exhibit the same reaction mechanism (same Tafel slope, b), but a higher current for the latter. This is clearly due to the rougher surface of sandblasted Ni, that is, to purely geometric effects. The third sample is Raney Ni. This is obtained from an alloy of Ni with Zn or A1 that are then leached away in alkaline solution [47-49]. This leaves a very porous solid with intrinsically very small particle size. The figure shows that Raney Ni, in addition to a much lower overpotential for H 2 evolution, also exhibits a lower Tafel slope. This is clear evidence for the occurrence of electronic eflects (diflerent mechanism) together presumably with important geometric effects. 

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... 

Mizutani, S., Sakai, S.I. and Takatsuki, El. (1999) Effects of C02 in the air on leaching behavior of heavy metal from alkaline residues, in J. Mehu et al. (Eds.), Waste Stabilization and Environment 99, Villeurbanne, France, 13-16 April 1999, Proceedings of poster presentation, pp. 125-127. 

Various bituminous coals were demineralized by an experimental two-step leaching process in which the ball-milled coals were first treated with a hot alkaline solution and then with a dilute mineral acid. Different alkalis and acids were studied to determine their relative effectiveness. In addition, the effects of alkali concentration, treatment temperature, and treatment time were evaluated. Under the best conditions, the process reduced the ash content of the coals by 85-90% and the total sulfur content by 70-90%. As the temperature of the alkaline treatment was raised from 150 to 345 C, the removal of sulfur increased greatly whereas the recovery of organic matter declined. When a 1 M sodium carbonate solution was employed for the treatment, the recovery of organic matter was 91-97% for various coals treated at 250 C and 79-89% for the same coals treated at 300 C. 

The alkaline treatment step had a pronounced effect on what happened to the ash content of Cherokee coal when it was subsequently leached with acid. As Figure 2 indicates, HN03 leaching of the raw coal reduced the ash content by 63%. Pretreating the coal with alkali for short intervals at temperatures up to 200 C had little... 

Under our experimental conditions, nitric acid dissolved iron pyrite but not the hematite which was formed during the alkaline treatment step. More rigorous alkaline treatment conditions were more effective than less rigorous conditions for converting the iron pyrite into hematite which could not be easily removed by the nitric acid. Consequently, when rigorous alkaline treatment conditions were applied to Lower Kittanning coal, the residual hematite more than made up for the other minerals which were extracted so that the overall reduction in ash content for the two-step process was no better than for HNO, leaching alone. 

The preparation of a solution of soap by the reaction of fat with water in the presence of base was probably one of the earliest chemical processes discovered by humans. Although the details of this discovery are lost in antiquity, we can imagine early humans finding that water that had been in contact with wood ashes from the campfire could be used to remove grease from hands and other objects and that this water became a more effective cleaning agent as it was used. The water leaches some alkaline compounds from the ashes, and this basic water hydrolyzes the esters of the fat or grease to alcohols and soap. This is why the hydrolysis of esters under basic conditions is called saponification (the Latin word for soap is sapo). 

Knapp et al. [32] developed an extraction (leaching) method using TMAH for the bnal determination of I concentrations in food samples by ICP-MS and a catalytic technique. TMAH has proven to be an excellent medium for use with ICP-MS, and its high alkalinity makes it a very effective reagent for extraction. 

Thiamin is one of the more unstable vitamins. Various food processing operations may considerably reduce thiamin levels. Heat, oxygen, sulfur dioxide, leaching, and neutral or alkaline pH may all result in destmction of thiamin. Light has no effect. The enzyme is stable under acid conditions ... 

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