Silica biogenic silicate

Summary The possibility of direct synthesis of silicon oi anic compounds based on hydrolysis-resistant organic derivatives of silicon by using biogenic silica (from siliceous rocks) as a new raw material is discussed. The complex triethylphosphate with silica, the ammonium salts of tricatechol, and humic acids of monosilicic acids were obtained. Products were identified by proton magnetic resonance spectroscopy, IR spectrophotometry, or elemental analysis. 

The dynamics of the process of dissolution and sorption of biogenic silica from siliceous rocks, diatomite and opoka, has been studied. 

So, as we are the first to show, humic acids, being natural polyphenols, actively dissolve the biogenic silica of siliceous rocks, and we used the scheme of obtaining the ammonium salt of the tricatechol ether of monosilicic acid in order to understand the methods of synthesis of biogeochemically active SOC, formed from natural amorphous silica and polyphenols in natural systems. 

We obtained the ammonium salts of humic ether of monosilicic acid from biogenic silica of siliceous rock and silicates of clay. 

To conclude, it is necessary to note that the reaction ability of biogenic silica depends on its structure and solubility, determined by various factors. It has been found that soluble forms of silica could be stabilized by S - 7% of glycerin and catechol. It has been determined that the amorphous part of the biogenic silica of siliceous rocks formed the complex with triethylphosphate and actively reacts with polyphenols (the simple one, catehol and complex ones, humic acids), with formation of ethers. The silicon organic derivatives and complexes formed are inert to hydrolysis. 

When silica-depositing organisms die, the oi anic constituents of their cells decompose, and the polymeric silica originally deposited within and around these cells is released, usually in a particulate form. The sources, nature, and ultimate fate of this biogenic silica are the subjects of this chapter. The first section deals with biogenic siliceous deposits on land and the second with such deposits in the sea. 

A global map of quartz abundance is given in Figure 14.12. In this case, the contribution of quartz is presented as the contribution to the bulk sediment from which biogenic carbonate and silica have been removed. This map is very similar to the global distribution of dust presented in Figure 11.4, reflecting the importance of aeolian transport for this detrital silicate. 

Opal (or opaline silica) An amorphous silicate formed through the polymerization of silicic acid molecules. Though most is biogenic in origin, some forms as a result of diagenesis. 

Silicon isotope variations in the ocean are caused by biological Si-uptake through siliceous organisms like diatoms. Insofar strong similarities exist with C-isotope variations. Diatoms preferentially incorporate Si as they form biogenic silica. Thus, high 5 °Si values in surface waters go parallel with low Si-concentrations and depend on differences in silicon surface water productivity. In deeper waters dissolution of sinking silica particles causes an increase in Si concentration and a decrease of 5 °Si-values. 

Conley, D. (1988) Biogenic silica as an estimate of siliceous microfossil abundance in Great Lake sediments. Biogeochemistry 6, 161-179. 

The offshore advective flux for Si shown in Fig. 17.3 (30 X 10 mol d l) was calculated by difference, based on the total flux of dissolved Si supplied to the shelf system (32 X 10 mol Si d-1), the estimated deltaic burial rate (1-3 x 10 mol Si d ), and the nearshore particulate flux (0.1-0.7 x 10 mol Si d ). This advective flux is in good agreement with the results of Daley (1997), who estimated that 30 x 10 mol d of Si leave the shelf, based on seasonal field data and a multibox model for the shelf. Most of the silicate (94%) supplied to the shelf by external sources appears to be transported to the open ocean in either dissolved or particulate form. Approximately 36% of the Si leaving the outer shelf is in particulate form according to these calculations. Biogenic silica export may have contributed to the lack of closure in the Edmond et al. (1981) silicate budget for the shelf, although deltaic burial also remains as a potentially important sink. 

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