1. Viscosity properties of Latvian illite clays Agnese Stunda, Valentīna Stepanova, Vitālijs Lakevičs (RTU, Institute of General Chemical Technology) EUROCLAY 2011 1.Latvian Illite containing clays and silt fraction (< 63 μm) has the ability to increase the viscosity of suspension for multiple times. 2.The 30-35 % concentration of suspension is a critical point where concentration starts to rapidly increase – most likely forms a network of particle aggregates. 3.It was found that modifying clay suspensions with methylcellulose (0,1%) increases the structurization concentration. In the same time, modifying clay suspensions with sodium carbonate (0,1%) lowers the structurization concentration. 4.Practical importance of the obtained results is related to the new product development, which will enable using the local resources for manufacturing and promotion of a high quality cheap thixotropic material on Latvian and European markets. Conclusions Concentration of suspension, mas% Viscosity, Pa s Prometejs Introduction Viscosity is an important parameter to design application and technological treatment processes of any clay based suspension. Various clay minerals are used in products as emulsifying, thickening and anticaking agents because of their thixotropic and colloidal properties. The previous studies about Latvian clays are mainly to investigate clay properties for productig ceramics for building industry. The aim of this study was to investigate the viscosity properties of Latvian clay suspensions with various clay compositions. Methods Clay suspensions were prepared from clay samples which were mechanically cleared from additions, crashed in a mortar, dispersed and swollen in a distilled H 2 O for 1 month. Swollen clays in suspension form were sieved and dried in 100 0 C temperature, by that obtaining a fine clay and silt fraction with the particle size < 63 μm. The qualitative and quantitative data about mineral composition were obtained in X-ray powder diffraction pattern analysis. Thixotropic properties of clay were researched by measuring relative viscosity of clay in water suspensions. Relative viscosity is measured with a hopper method. The dynamic viscosity of the clay suspensions were measured by rotational viscometer Fungilab EXPERT series. It was found that, with a suspension concentration increasing, a clay suspension’s dynamic viscosity also increases. It happens until the moment when the viscosity increases significantly, a dramatic rise is shown on the curve. It proves that the clay particles form a lace-like, easily breakable structure and demonstrate thixotropic properties. Also these clays can be classified as pseudoplastic – the viscosity value decreases with increasing shear rate. The border point for all clay samples is approximately at the same concentration level – 35 mas %, however the rise of viscosity differs. Thixotropic properties of clay suspensions are amended, modifying the samples with sodium carbonate (Na 2 CO 3 ) and methylcellulose. It is defined that modification of clay suspensions with methylcellulose (0,1%) increases concentration of structurization. However, modification of clay suspensions with sodium carbonate (0,1%) lowers concentration of structurization. While mixing sodium carbonate with a clay sample, there is almost no exchange of Са 2+ onto Na +. Their interaction occurs only after putting clay powder in the water, but mechanically adsorbed salts weakly interacts with clay particles. Methylcellulose is a highly molecular organic soluble material. It gives a serious impact on the contents of water. Breaking the contents of clear water by its hydrophilic fragment and structuring it with hydrophobic groups, it structurizes the water around itself in a specific way by forming thixotropic systems Results and discussion Locations of clay deposits Strēļi + modifiers Ceplīši Ugāle Prometejs Strēļi Pavāri Period Quartar: Prometejs, Ugāle, Ceplīši Jurassic: Strēļi Devon: Pavāri.