Description of the invention The present invention relates to a method for extraction of silica (Si02) and magnesium compounds (MgC03, MgO, Mg (OH) 2, MgS04, MgC12) from the mineral olivine (Mg2SiO4) by chemical and thermal tratment.

The use of percipitated silica within filler markeds, including plastic, paint, sealant and the rubber tire industry, has during the last ten years increased considerably. The total consumption of percipitated silica in world maeked extends 1 million tons per year. And a continuing increase of consumption within the filler markeds will result in a need of increased production capacity.

Concerning magnesium compounds is the refractory industry dominating consuming 65% of the total demand. Other important markeds are the chemical industry, the water treatment sector and the use within different environmental areas. The total consumption of magnesium compounds is approx. 10 million tons of MgO per year. The magnesium metal industry is hereby only a modest consumer, with a demand of approx. 500.000 tons per year. The raw materials used for production of magnesium compounds are mainly magnesite (MgC03) counting for approx. 80% of the raw materials in use, while sea water (0.13% MgO) The main consumption of percipitated silica in the world marked is covered thruogh complex production processes involving high investment and operating costs, resulting in a high cost product.

MgO in the refractory industry is mainly considered as a commodity product marked where prices are based on offer and demand.

As possible interferings, the following patent documents have been examined: (1) NO 177137 (corresponding to"US Patent No 5,780,005") (2) NO 143583 (3) NO 160200 (4) AT 352684 (5) JP 60161320 Examening the above listed patent documents, the methodes described shows that the olivine minerals are leached in aqueous solutions of mineral acids in acid baths, involving that the dissolving process of the olivine mineral and the formation of silica takes place in an acid bath at a mxiumum temperature of 110°C. These methodes involved results in the formation of a silica-gel, where a small part of solids binds a large volume of liquid. A main problem combined with a use of the known technology is the formation of silica-gel, which restricts or excludes efficient filtering and thereby excludes a practical use of technology.

The present invention is described by mixing ground olivine sand with concentrated sulphuric acid at a weight ratio olivine/sulphuric acid of 1-0.3, to a slurry, which by thermal treatment is heated to temperatures between 150°C-400°C, ideally 250°C, over a period of time ranging between 3-12 hours, ideally 7-8 hours. This treatment may more precisely be characterized as a sulphating process. Combined with the thermal treatment, the mixture forms a dry aggregate product, which then is dissolved (leached) in water. It is hereby achieved to pecipitate silca solids spontaneous without gel formation, where the rest solution consists of aqueous magnesium sulphate.

As described is the present invention of significant difference from other known technologies, first by the present treatment method which more precise is characterized as sulphating and where known technologies are presented as acid leaching, and second that the temperatures involved in the present sulphating process demands significant higher degrees compared with the known leaching methodes. It is also of significance that the silica end product in the present invention results in the formation of a non gel silica, while the known methodes results in silica gel formation which restricts a practical use of the methodes. The examined patent documents are therefor not considered to be of relevant interference to the present invention.

The present invention concerns manufacturing of silica and magnesium compounds based on ground olivine, where the mineral olivine ideally is recommended to contain 48-50% MgO.

The invention relates to a method for manufacturing silica (Si02) and magnesium compounds (MgO, MgC03, Mg (OH) 2, MgS04, MgC12), based on the mineral olivine ( (Fe, Mg) 2Si04), characterized wherein olivine is mixed with concentrated sulphuric acid at a weight ratio olivine/sulphuric acid of 1-0. 3, and by heating the mixture between 150°C-400°C, giving the mixture a reaction time between 3-12 hours, and thereafter dissolve (leach) the mixture in water, whereby silica percipitatites to a solid and then is removed from the solution by filtration, where the filtrate containing dissolved magnesium is further processed to magnesium compounds, and where the silica filter product is further washed with a weak solution of soda (NaC03) or sodium hydroxide (NaOH) and thereafter eventually further washing of the silica with a weak aqueous solution of an acid or a mixture of acids, in order to obtain a pure silica (solid) which is filtered out as a silica product.

It is hereby achieved to manufacture a silica product with significant identical characteristics compared to precipitated silica, through a relative simple process at a relative low cost.

After filtering out the silica solids, the rest solution is treated seperately, which more specified is described by a first step neutralization of excess acid with ground limestone (CaC03), until a weak sour or neutral solution is obtained, whereby percipitated gypsum (CaS04) is filtered out. The restsolution is then treated by"solvent extraction"process (Elkem method) whereby iron (Fe) is removed from the solution. The restsolution is then blown through with C02 gas whereby MgC03 is percipitated and filtered out (Pattison method). MgC03 may then be transfered to calcination for manufacturing of MgO. The filtrate may then be transfered to a waste treatment plant eventually to a seperate plant for manufacturing of nickel and chromium compounds.

Example The starting material used was olivine sand APS 120 (49-50% MgO) which was ground down to 70% minus 0.044mm in a ball mill. The material had the following chemical analysis: Si02 41.5-42.5% Fe203 6.8-7.3% Cr203 0.2-0.3% Api203 0.4-0.5% NiO 0. 3-0.35% MnO 0.05-0.1% CaO 0. 05-0.1% MgO 49. 0-50.0% The ground olivine sand was mixed with concentrated sulphuric acid (H2SO4) at a weight ratio olivine/sulphuric acid of 0.5 and heated to 250°C. The mixture was given a reaction time of 8 hours at a constant heat of 250°C. The sulphated mixture was then dissolved in water (approx. at 12 weight % solids) during a stirring period of 30 minutes. The solid silica product was thereafter filtered out, while the filtrate was stored in a separate container. The solid silica product was then mixed with a 5% soda solution at a weight of 12%. The purified silica product was thereafter filtered out while the restsolution was stored in a waste material container. The purified silca was then mixed with water (12% solids by weight) during a stirring period of 30 minutes as the last cleaning step. The purified silica was thereafter filtered off and dried. The rest solution was stored in a separate waste container. The dried silica product had the following analysis.

Si02 96% MgO 3.50% BET 100kv. m/g The analysis shows that the silica product obtained can be identified and classified as percipitated silica. An additonal cleaning step of the silica could involve further washing with a weak solution of a 1-2% HCL + HF, in order to dissolve excess impurities.

The restsolution from the first leaching step with water, which after filtering out the silica, leaves a solution containing mainly dissolved magnesium in addition to minor part of dissolved iron, chromium, nickel and aluminium together with excess sulphuric acid from the main reaction, is first neuteralized with lime. Percipitated gypsum is filtered out, whereafter iron is extracted from the filtrate by the Elkem method. The filtrate then containing mainly dissolved magnesium and minor parts of nickel, chromium and aluminium is treated with carbondioxide gas, resulting in formation of dissolved magnesium-bicarbonat (Mg (HC03) 2.

Heating of the magnesium-bicarbonate solution, leads to formation of magnesium carbonate solids (Pattison method), which is filtered out and dried. The described process illustrates how production of syntetic magnesite (MgC03) takes place, which corresponds to the main material source for magnesium compounds.