Vermiculite concentrate

Vermiculite Concentrate (also raw or unexfoliated vermiculite)—The mineralogical name given to hydrated laminar magnesium-aluminum-iron silicate (Mg,Ca,K,Fe(II)3(Si,Al,Fe(III)40io(OH)204H20) minerals, which resemble mica in appearance. This mineral has the unusual property of exfoliating or expanding to a low density, bulky material when heated (see Vermiculite). 

The photograph in Figure 2 shows a sample of raw vermiculite ore from Libby, Montana, with asbestiform amphibole fibers mixed in with the vermiculite. Figure 3 shows processed vermiculite concentrate (before expansion) and exfoliated vermiculite (after expansion). 

Figure 3. Photograph of vermiculite concentrate (on the right) and exfoliated vermiculite (on the left). Source U.S. Geological Survey and U.S. Environmental Protection Agency, Region 8, Denver, Colorado.

In an early EPA-supported study, -21% to 26% of the weight of raw ore samples and 0.3% to 7% of the weight of vermiculite concentrate samples from Libby were accounted for by asbestiform amphibole identified as tremolite-actinolite (Atkinson et al. 1982). In a 1984 study of samples from Libby, Montana, conducted by W.R. Grace, asbestiform amphibole percentage by weight varied from 3.5% to 6.4% in raw ore and from 0.4% to 1.0% in the concentrate (cited in Amandus et al. 1987a). 

Non-Metals, Inc., Affiliate of The China National Non-Metallic Minerals Group, Tucson, AZ, USA Chine Vermiculite Concentrate TG series - golden color, KV series - silver color Strong-Lite, Pine-Bluff, AR, USA... 

Vermiculite concentrate - Since the objective of nearly all vermiculite production is the expanded form, the principal product of vermiculite mining is a vermiculite concentrate. Vermiculite ores typically contain only about 35% vermiculite. The balance may consist of various proportions of mica, chlorite, and other sheet silicates. The ore is beneficiated to vermiculite flake concentrates of at least 90% purity by either dry or wet processes. The former include screening and air separation, while the latter may employ either froth... 

Once a layer-silicate clay forms, it does not necessarily remain in the soil forever. As conditions change it too may weather and a new mineral may form that is more in equilibrium with the new conditions. For example, it is common in young soils for the concentrations of cations such as K, Ca, or Mg in the soil solution to be high, but as primary minerals are weathered and disappear, cation concentrations will decrease. With a decrease in solution cations, a layer-silicate such as vermiculite will no longer be stable and can weather. In its place. 

Other studies use soil or sediment samples for a more accurate indication of microbial activity in natural environments. In these samples, organic matter and clay particles play a role in metal toxicity.76112113 Both organic material and clay particles in soil can bind metals and reduce their bioavailability. For example, Pardue et al.87 demonstrated that much less solution-phase cadmium was required to inhibit trichloroaniline (TCA) dechlorination in a mineral-based soil than in a soil containing a higher concentration of organic matter. Other studies have shown that adding clay minerals to a medium mitigates toxicity. Clay minerals, such as kaolinite, montmorillonite, bentonite, and vermiculite, can bind to metals to decrease the amount that is bioavailable.112 115... 

After sealing the head, the exterior of the drum shall be decontaminated and then labeled IAW EPA and DOT regulations. All leaking containers shall be overpacked with vermiculite placed between the interior and exterior containers. Decontaminate and label IAW EPA and DOT regulations. Dispose of the material IAW waste disposal methods provided below. Dispose of material used to decontaminate exterior of drum IAW Federal, state and local regulations. Conduct general area monitoring with an approved monitor (see Section VIII) to confirm that the atmospheric concentrations do not exceed the airborne exposure limit (see Sections II and VIII). 

Our model for the adsorption of water on silicates was developed for a system with few if any interlayer cations. However, it strongly resembles the model proposed by Mamy (12.) for smectites with monovalent interlayer cations. The presence of divalent interlayer cations, as shown by studies of smectites and vermiculites, should result in a strong structuring of their primary hydration sphere and probably the next nearest neighbor water molecules as well. If the concentration of the divalent cations is low, then the water in interlayer space between the divalent cations will correspond to the present model. On the other hand, if the concentration of divalent cations approaches the number of ditrigonal sites, this model will not be applicable. Such a situation would only be found in concentrated electrolyte solutions. 

Carbon tetrachloride slowly reacts with hydrogen sulfide in aqueous solution yielding carbon dioxide via the intermediate carbon disulfide. However, in the presence of two micaceous minerals (biotite and vermiculite) and amorphous silica, the rate transformation increases. At 25 °C and a hydrogen sulfide concentration of 0.001 M, the half-lives of carbon tetrachloride were calculated to be 2,600, 160, and 50 d for the silica, vermiculite, and biotite studies, respectively. In all three studies, the major transformation pathway is the formation of carbon disulfide. This compound is... 

If the cations of variable valency (e.g., Fe2+/Fe3 + ) are present in not too low concentrations, the crystals will be semiconductors. In non-equilibrium vermiculites, the internal electric field is then strongly influenced by their electronic conductivity, as explained in Section 4.4.2. If we start with an equilibrium crystal and change either pH, ae, aor a, (where i designates any other component), coupled transport processes are induced. The coupling is enforced firstly by the condition of electroneutrality, secondly by the site conservation requirements in the T-O-T blocks (Fig. 15-3), and thirdly by the available free volume in the (van der Waals) interlayer. It is in this interlayer that the cations and the molecules are the more mobile species. However, local ion exchange between the interlayer and the relatively rigid T-O-T blocks is also possible. 

Thus, ion exchange kinetics on heterogeneous surfaces such as vermiculite involve mass transfer (PD and FD) and CR processes (Fig. 5.2). For actual CR to occur, ions must be transported to the active fixed sites of the particles. The film of water adhering to and surrounding the particle and the hydrated interlayer spaces in the particle are both zones of low concentration. These zones are constantly being depleted by ion adsorption to... 

Recently, it was noted that the addition of poly(vinyl methyl ether) to a clay-salt-water system induced the contraction of the interlayer separation between the clay platelets [18], The K-butylammonium vermiculite used in those experiments provided an ideal structure of regularly spaced and parallel charged colloidal platelets in a salt solution [19,20], Swenson et al. [21-23] studied the effect of the addition of poly(ethylene oxide) (PEO) on the distance between the vermiculite layers and observed that, with increasing PEO concentration, the distance between the vermiculite layers decreased. They estimated that the bridging force per bridge was 1.4 pN. 

Fig. 16. The interlayer separation of n-butylammonium vermiculite against the volume fraction of PVME. The experimental data are from Fig. 4 of Ref. [18]. The values of the parameters employed in the calculation were T= 8 C C, the salt concentration is 0.1 M, <3=1.88 nm, the Hamaker constant between the plates h=1x10-19 J, the Hamaker constant between the segments and plates =1 x 10—20 J, c=—0.035 C/m2, v=300 A3, =83.

---