In-Tank-Precipitation

Manganese (IV) oxide enjoys numerous applications in modem technologies. The most widely known areas of its usage are sorption processes one could recall that co-precipitation of contaminating cations with manganese oxide is still employed as part of the in-tank precipitation in processes of treatment of supernatant wastes at high concentration. Furthermore, co-precipitation data are usually used as benchmark results in studies of novel sorbents for strontium [4],... 

These materials have been used for in-tank precipitation at the Savannah River Site in the... 

The largest use of calcium hypochlorite is for water treatment. It is also used for I I and household disinfectants, cleaners, and mildewcides. Most of the household uses have been limited to in-tank toilet bowl cleaners. In areas where chlorine cannot be shipped or is otherwise unavailable, calcium hypochlorite is used to bleach textiles in commercial laundries and textile mills. It is usually first converted to sodium hypochlorite by mixing it with an aqueous solution of sodium carbonate and removing the precipitated calcium carbonate. Or, it can be dissolved in the presence of sufficient sodium tripolyphosphate to prevent the precipitation of calcium salts. However, calcium hypochlorite is not usually used to bleach laundry and textiles because of problems with insoluble inorganic calcium salts and precipitation of soaps and anionic detergents as their calcium salts. 

Modem manufacturing processes quench the roast by continuous discharge into the leach water held in tanks equipped with agitators. At this point the pH of the leach solution is adjusted to between 8 and 9 to precipitate aluminum and siHcon. The modem leaching operations are very rapid because no or htde lime is used. After separation of the ore residue and precipitated impurities using rotary vacuum filters, the cmde Hquid sodium chromate may need to be treated to remove vanadium, if present, in a separate operation. The ore residue and precipitants are either recycled or treated to reduce hexavalent chromium to Cr(III) before disposal. 

The condensed reaction mixture is evaporated in film evaporator 16 under vacuum. The crude l-(2,6-dimethyl)-phenoxy-2-aminopropane hydrochloride is precipitated in tank 17 using HCl dissolved in organic solvent //, separated in centrifuge 18, and dried in tray drier 19. The final purification by crystallization from solvent III occurs in crystallizer M. Pure l-(2,6-dimethyI)-phenoxy-2-amino-propane hydrochloride is separated in centrifuge 21 and dried in tray drier 22. The plant is equipped with typical solvent recovery and storage facilities not shown in the figures. 

The first step in the precipitator is the addition of polyelectrolyte solution in the flash mix tank [T-98], surge tank [T-99], and then into the slow mix unit [T-100] containing a variable speed mixing paddle. The purpose of this unit is to coagulate and flocculate53 the metal hydroxide precipitates. 

Mass balance measurements for 41 elements have been made around the Thomas A. Allen Steam Plant in Memphis, Tenn. For one of the three independent cyclone boilers at the plant, the concentration and flow rates of each element were determined for coal, slag tank effluent, fly ash in the precipitator inlet and outlet (collected isokinetically), and fly ash in the stack gases (collected isokinetically). Measurements by neutron activation analysis, spark source mass spectroscopy (with isotope dilution for some elements), and atomic adsorption spectroscopy yielded an approximate balance (closure to within 30% or less) for many elements. Exceptions were those elements such as mercury, which form volatile compounds. For most elements in the fly ash, the newly installed electrostatic precipitator was extremely efficient. 

In 2001, the SRS announced its choice of CSSX as the baseline cesium-removal technology over small-tank precipitation (a small-scale version of the ITP process) and ion exchange with CST for its Salt Waste Processing Facility (SWPF) to go into operation in 2010 [22], An optimized solvent system, model, and flowsheet were developed and demonstrated in 2001 and 2002 [37,49], and a modular concept was developed by ORNL in 2003 [68], Thus, the past decade has seen the emergence and maturation of a powerful new technology based on a macrocyclic cation receptor designed to function in solvent extraction to meet the critical need of the USDOE for a means of cleanly separating Cs from alkaline tank waste. 

The lower acidity obtained in the plant-scale run resulted in the precipitation of a small amount of an iron organophosphate material which could be dissolved at 50°C in 0.5M HNO3. Therefore, after moving the solution to the hold tank, the denitration evaporator was flushed with 1M HNO3. This flush raised the acid concentration of the prepared solution to 0.37M and the volume to 2700 L. 

Two precipitation conditions were investigated with either dysprosium or samarium as a stand-in for Am. Both conditions were based on physical limitations on the volumes in tanks to be used in the Am solution processing. The denitrated product... 

Recovery of Americium—Curium From High-Activity Waste Concentrate by In-Canyon-Tank Precipitation as Oxalates... 

Washing the Precipitated Oxalates. As a result of the 2500-L heel of slurry left in the precipitation tank, the product slurry contained large concentrations of contaminating cations. To yield an acceptable product for downstream processing in MPPF, these ions had to be diluted from the product. Five equal volume washes of the slurry were calculated to reduce the non-lanthanide impurity concentrations of polyvalent cations to acceptable levels only four washes are needed to reduce the monovalent cations to acceptable levels as shown in Tables 1 and 2. 

The simplest continuous reactor to consider is that of a constantly stirred tank reactor (CSTR) or precipitator, also called a mixed suspension, mixed product removal crystallizer (MSMPR) [98], shown in Figure 6.23. This tsrpe of precipitator has a constant volume, V, with an input flow rate equal to its output flow rate, Q. The population iJofR) in the precipitator is that which leaves as product. In this case, the population balance is used at steady state (i.e., drjfjdt — 0) ... 

The HLW solutions obtained by reprocessing are collected in tanks near the reprocessing plants. They contain relatively high concentrations of HNO3 which can be decomposed by addition of formaldehyde or formic acid. At low acid concentrations, however, hydrolysis and precipitation of elements of groups III and IV occurs. Concentration by heating may lead to volatilization of fission products, such as Ru isotopes in the form of RUO4. 

---