Zirconate additives

Hydrozirconation usually takes place readily at or slightly above room temperature, in benzene or toluene. The reactivity pattern of alkenes in hydrozirconation is the same as in hydroboration, except that tetrasubstituted alkenes are unreac-tive.457,460 A unique feature of hydrozirconation of alkenes is that, with some exceptions, terminally zirconated addition products are formed exclusively. Since isomeric alkenes cannot be isolated, zirconium moves rapidly along the chain without dissociation. Tertiary zirconium intermediates seem to be so unstable that the isopropylidene group never undergoes hydrozirconation [Eq. (6.75)],460 and hence, 1-methylcyclohexene fails to react.460 The reason is apparently steric, since the alkene must fit into the somewhat bent sandwich structure of the reagent (41) ... 

Minor amounts of thermally stable neoalkoxy titanate and zirconate additives may provide a means for postreactor, in situ metallocene-like repolymerization catalysis of a filled or unfilled polymer during the plasticization phase. This may result in the creation of metallocene-like (titanocene or zirconocene) behavior associated with effects such as increased composite strain to failure resulting in increased impact toughness or enhanced polymer foamabUity. Other effects to be discussed below with specific examples are related to enhanced processability, reduced polymer chain scission, shortened polymer recrystallization time, and compatibilization of dissimilar polymers. 

Simple ABO compounds in addition to BaTiO are cadmium titanate [12014-14-17, CdTiO lead titanate [12060-00-3] PbTiO potassium niobate [12030-85-2] KNbO sodium niobate [12034-09-2], NaNbO silver niobate [12309-96-5], AgNbO potassium iodate [7758-05-6], KIO bismuth ferrate [12010-42-3], BiFeO sodium tantalate, NaTaO and lead zirconate [12060-01 -4], PbZrO. The perovskite stmcture is also tolerant of a very wide range of multiple cation substitution on both A and B sites. Thus many more complex compounds have been found (16,17), eg, (K 2 i/2) 3 ... 

In addition, uranium and lead transport mechanisms ia radioactive minerals have been studied ia order to evaluate the suitabiUty of mineral phases as hosts for radioactive wastes. Zircon is one of the most commonly used geochronometers, as well as a proposed nuclear waste matrix material, and there are many mechanisms by which uranium and lead can migrate through its stmcture (19). 

Oxide Chlorides. Zirconium oxide dichloride, ZrOCl2 -8H2 0 [13520-92-8] commonly called zirconium oxychloride, is really a hydroxyl chloride, [Zr4(OH)g T6H2 0]Clg T2H2O (189). Zirconium oxychloride is produced commercially by caustic fusion of zircon, followed by water washing to remove sodium siUcate and to hydrolyze the sodium zirconate the wet filter pulp is dissolved in hot hydrochloric acid, and ZrOCl2 -8H2 O is recovered from the solution by crystallization. An aqueous solution is also produced by the dissolution and hydrolysis of zirconium tetrachloride in water, or by the addition of hydrochloric acid to zirconium carbonate. 

Heat aging characteristics may be improved by the addition of a few per cent of ferric oxide and barium zirconate to name but two materials mentioned in the literature. 

In addition to pure oxides, oxidic minerals and ores also can be converted to metal chlorides. Examples include minerals such as zircon, bastnasite, monazite, ilmenite, etc. 

Other additives such as silanes, titanates and zirconates are also used to overcome the processing characteristics of silica fillers. Silanes not only give improved processability of silica-filled compounds, but also provide improved crosslinks between the silica particle surface and the rubber molecular chains giving increased physical properties. The use of silane coupling agents at a... 

The above intramolecular diene cyclizations are likely to proceed through a similar set of reactions as shown in Scheme 6.2 for the intermolecular variants. Thus, as depicted in Scheme 6.6, formation of the zirconacyclopropane at the less hindered terminal alkene (—> ii), generation of the tricyclic intermediate iii, Zr—Mg exchange through the intermediacy of zirconate iy and 3-H abstraction and Mg alkoxide elimination in v may lead to the formation of the observed product. Additional kinetic and mechanistic studies are required before a more detailed hypothesis can be put forward. 

Some deposits in addition to REO contain zircon and titanium minerals. From these ores, REO and zircon can be recovered in bulk concentrate suitable for hydrometallurgical treatment. 

The sulphosuccinamate collector was extremely effective in flotation of rutile, as well as ilmenite and zircon from a fine sand deposit. Laboratory testing conducted on Wimmera heavy mineral sand from Australia indicated that the use of sulphosuccinamate achieved a high titanium recovery in the bulk cleaner concentrate. Table 25.4 shows the results obtained on the Wimmera heavy mineral sand. The sand was scrubbed and deslimed before flotation. Between 90% and 95% Ti02 was recovered using a 60g/t addition of succina-mate collector. 

Over the past 20 years, a new technology was developed that can produce a high-grade rutile concentrate from hard rock ores. In addition, different methods have been developed by which rutile from bulk gravity concentrates containing zircon and other heavy minerals can be successfully separated. 

The fine -250-mesh product was preconcentrated using gravity (tabling) followed by zircon flotation and magnetic separation to produce rutile and ilmenite concentrate. The process flowsheet with points of reagent additions is presented in Figure 25.14. Using... 

Figure 25.14 Plant flowsheet with reagent additions for production of zircon, rutile and ilmenite from the Sierra Leone fines.

The bulk flotation can be accomplished with the addition of small doses of oleic acid plus oxidized emulsion of fuel oil. The fuel oil is treated with 10% solution of NaOH at a temperature of 60-80°C for 1 h. The following method was used for rutile-zircon separation the concentrate was thickened, followed by heat conditioning to 60°C. After the heat treatment, the zircon was floated without the addition of collector. The zirconium tailing is the rutile concentrate. The zircon concentrate was thickened, followed by gravity cleaning. In some cases, the heat-treated pulp is washed before zircon flotation. The following metallurgical results were obtained ... 

Method 2- It involves bulk flotation of rutile, ilmenite and zircon followed by selective flotation of mtile and ilmenite and depression of zircon. Figure 25.16 shows the flowsheet with type of reagent additions used in selective flotation of titanium from zircon. 

Figure 25.16 Flowsheet and reagent additions used in selective titanium flotation and zircon depression.

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