Nano-structured silicas and silicates––new materials and their applications in paper

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Abstract

Nano-structured silica with an open network structure has been produced by controlled precipitation from geothermal water. The material has a pore volume, as measured by the oil absorption capacity of about 200–250 g oil. 100 g−1 silica, and the surface area is about 50–60 m2 g−1. It has been used as a filler in newsprint and the technology has been developed on a laboratory scale and progressed to pilot plant production with full scale paper mill manufacturing and commercial printing trials. Print through reductions of 30% for newsprint and 40% for yellow directory grade paper were achieved. Nano-structured calcium silicate with an open framework structure has been formed from sodium silicate solution. This product has a very large pore volume of about 300–550 g oil. 100 g−1 silicate and a large surface area of about 350–600 m2 g−1 depending upon the synthesis method. It has been tested as a filler in newsprint on a laboratory scale and reduced print through by about 40% for 55 gsm newsprint and by about 53% for 45 gsm newsprint. The material is better than nano-structured silica for this application and it substantially outperforms calcined clay.

Introduction

Silicas and silicates in their various crystalline macro forms are ubiquitous as minerals and rocks that make up the earth's crust. These are produced by crystallization from silica-containing solutions or melts, or by subsequent geochemical alteration, in accordance with the natural conditions that prevail at the time. Geothermal waters which are cooled at the surface are typically supersaturated in dissolved silica, which progressively precipitates out in an uncontrolled manner, to form amorphous silica sinters. However, by careful control of the precipitation using either a natural (e.g. geothermal water) or a synthetic (e.g. sodium silicate solution) source of silica, it is possible to produce a number of nano-structured silica and silicate materials with specific characteristics, properties and chemical functionality that are not found in nature. This provides the opportunity to produce new functional materials from a commonly available resource [1], [2], [3], [4], [5].

Section snippets

Formation and characterisation

In geothermal water which has a pH = 7–9, the dominate silica species is the silicilate ion H3SiO43− or Si(OH)3O3− which can react with undissociated silicic acid monomers Si(OH)4 or other silicilate ions to produced polymeric hydroxy silica chains which polymerise further to form hydrous silica sol particles of about 4–8 nm diameter.Si(OH)4+Si(OH)3O3−→(HO)3SiOSi(OH)3+OH(HO)3SiOSi(OH)3+Si(OH)3O3−→(HO)3SiOSi(OH)2OSi(OH)3+OH

This process takes place in a number of stages as depicted in Fig. 1. The

Nano-structured calcium silicate

Nano-structured calcium silicate is produced by a proprietary method from geothermal water or a sodium silicate solution. The resulting product is a proprietary material comprising an open framework structure made up of nano-size platelets (Fig. 3), which affords a very large pore volume of about 300–550 g oil. 100 g−1 silicate and a large surface area of about 350–600 m2 g−1 depending upon the synthesis method.

These properties are considerably enhanced over those of the nano-structured silicas.

Conclusion

The unwanted silica deposition in geothermal resource utilisation can be obviated by the controlled precipitation of a nano-structured silica product from the separated geothermal water to provide a product with a network structure that can be used as a filler in newsprint and directory grade paper to reduce print through and enhance the print and optical properties of the paper. A related nano-structured calcium silicate product with an open framework structure can be formed from sodium

References (5)

  • J.H. Johnston, R.T. Harper, N. Wiseman, The Controlled Precipitation and Use of Amorphous Silica from Geothermal Fluid...
  • R.T. Harper, J.H. Johnston, S.G. Keyte, T.J. Gresham, The use of geothermal silica to improve newsprint quality at...
There are more references available in the full text version of this article.

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