Calcium sulfate activity with added

Chemically pure reagents were used. Cadmium was added as its sulfate salt in concentrations of about 50 ppm. Lanthanides were added as nitrates. For the experiments with other metal ions so-called "black acid from a Nissan-H process was used. In this acid a large number of metal ions were present. To achieve calcium sulfate precipitation two solutions, one consisting of calcium phosphate in phosphoric acid and the other of a phosphoric acid/sulfuric acid mixture, were fed simultaneously in the 1 liter MSMPR crystallizer. The power input by the turbine stirrer was 1 kW/m. The solid content was about 10%. Each experiment was conducted for at least 8 residence times to obtain a steady state. During the experiments lic iid and solid samples were taken for analysis by ICP (Inductively Coupled Plasma spectrometry, based on atomic emission) and/or INAA (Instrumental Neutron Activation Analysis). The solid samples were washed with saturated gypsum solution (3x) and with acetone (3x), and subsequently dried at 30 C. The details of the continuous crystallization experiments are given in ref. [5]. 

The addition of sulfates to the positive plate was evaluated by Lorenz (as described in Ref. 58). Results showed that 0.5wt.% barium sulfate or strontium sulfate added to the positive active-material reduced the cycle-life from 100 cycles without the additive to 30-50 cycles with the additive under the same conditions. The end-of-life was taken as a 40% decline in the initial capacity. Lorenz further reported that calcium sulfate is not isomorphous with lead sulfate and therefore has no effect on battery life. (Note, calcium sulfate also does not act as an inorganic expander for negative plates.)... 

It has been suggested that sulfobelitic blended cements could be produced by combining sulfobelitic clinkers with granulated blast furnace slag or fly ash, in addition to calcium sulfate (Sudoh et al, 1980 Beretka et al, 1992, 1993). Such an approach makes little sense, however, because calcium hydroxide is virtually absent among the hydrates formed, and the pH of the pore solution is relatively low. Under these conditions the added fly ash cannot undergo a pozzolanic reaction, and the hydraulic activation of the slag is insufficient. 

AFBC ashes exhibit hydraulic properties. The main reaction products are a C-S-H phase and ettiingite formed in a reaction of the thermally activated clay minerals with the present free lime, calcium sulfate, and mixing water. PFBC ashes are similarly reactive however, calcium oxide or calcium hydroxide must be added to the system to compensate for the lack of sufficient amounts of free lime in the ash. 

Selection of stationary phases is, therefore, limited for these preparative techniques. The only materials which can be used are those for which an additional amount of binder endows the necessary stability and does not impair the separation these can be silica, kieselguhr, alumina, plaster of Paris (76), and their combinations. In general, silica gel of TLC quality (15 pm average particle size) with gypsum binder is used with additional binder, 3.5% calcium sulfate hemihydrate. If other types of silica without binder are used, approximately 20% of the binder must be added. It is reconunended that several layers be prepared together and stored in a safe place. They can be activated before use. Precoated glass rotors (1,2, or 4 mm layer thickness) are available from Analtech (Newark, Delaware, USA). 

After the concentrate was filtered, washed and dried it was heated to 1100°C for 15 min to form 3-spodumene. The roasted ore was then cooled, mildly crushed, a 50% excess of 93% sulfuric acid added and the mixmre heated to 250°C for 15 min. The reacted mass was next cooled and then leached with water at room temperature. A 97% yield of lithium in the (3-spodumene was obtained, and lime was added to the leach solution to neutralize the excess sulfuric acid, raise the pH to 6.5 and precipitate most of the iron, aluminum and sulfate. The slurry was filtered and the pH raised to 12.0 by the addition of a small amount of soda ash to precipitate the calcium. This mixture was filtered, some activated carbon added to remove organics, the solution was refiltered and the pH reduced to 7.0 with sulfuric acid. The clear solution was then evaporated to 200 g/liter lithium sulfate concentration. Finally, soda ash was added to the strong, hot solution to precipitate lithium carbonate. When filtered, washed and dried analysis showed >98% Li2C03, with the impurities listed... 

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