There are some cement grinding aids

There are some cement grinding aids (CGA) include triethanolamine (TEA), mono- and diethylene glycol (DEG), oleic acid, sodium oleic, dodecylbenzene sulfonic acid, and sodium lignosulfonic acid (from paper industry) (Sottili; L. et al 2002), sugarcane bagasse ash (Cordeiro; G.C. et al,2009), beet molasses( Gao; X. et al, 2011), triethanolamine (TEA) with potassium hydroxide (Heinz; D. et al 2010), dihydroxy compound class (ethylene glycol, propylene glycol, and polypropylene glycerol), phenol, glycol, alkanol amine , alcohols and glycols( Hasegawa;M. et al 2011), fatty acids(Albayrak; A.T. et al 2005). Katsioti et al 2009 also investigated the impact of some various cement grinding aids such as triethanolamine hydrochloride, triethanolamine, 2,4pyrimidinedione,1,1′,1″-Nitrolotri-2-propanol (TIPA), 1,1’Iminobisi-2-propanol (DIPA), 4-hydroxy-1,8-naphthyridine, benzene, and benzene amine on grind ability and cement performance. Glycerol resulted from jatropha biodiesel industry has similar physical and chemical properties as mono-ethylene glycol (EG) and diethylene glycols (DEG) that make it possible to use as grinding aids. A significant reduction of energy consumption can be noticed during the grinding of Portland cement clinker and gypsum by adding a small quantity of a grinding aid (GA) in the range of about 0.02- 0.10 % of the manufactured cement weight inside the cement mill. The chemical basis of the used GAs includes ethanol mines such as triethanolamine (TEA), monoethanolamine (MEA) and tri isopropanol amine (TIPA), as well as glycols such as ethylene glycol (EG) and propylene glycol (PG) can be considered the main factor.

Because of their highly organic polar nature, GAs are adsorbed on surfaces formed by the fracture of electrovalent bonds (i.e. Ca–O and Si–O), leading to reducing the surface energy forces that cause attraction and re-agglomeration of the newly produced cement particles (Assaad et al., 2008). Approximately 95% of the feed to the cement grinding circuit is clinker and the rest of the feed are ”additives” which includes grinding aids (GAs). The quality of cement is measured by the surface area (Blaine index). It should be noticed that the surface area of the cement powder depends on the size distribution of cement particles (smaller particles have a larger surface area) (Jankovic, A. et al, 2004).

The formation of electrostatic surface charges of opposed polarity causes the cement particles to agglomerate as a result of the forces of attraction acting on them. Consequently, the cement particle agglomeration reduces the efficiency of the mill. This phenomenon is characterized by an increase in energy consumption whilst maintaining constant Blaine. The extent of agglomeration depends on:

• The specific characteristics of the materials to be ground
• The operating parameters of the mill
• The efficiency and distribution of the grinding media
• The fineness of the cement particles,
• The internal operating conditions of the mill (humidity, temperature, ventilation, the condition of the armor plating, etc.).

The agglomeration phenomenon remains one of the priorities of cement manufacturers, hence the importance of grinding aids. The latter enables the partial neutralization of surface charges which have developed during milling. Additives, such as water, organic liquids, and some inorganic electrolytes have been used to reduce the surface free energy of the material being ground with a view to improving grinding efficiency (Sohoni, S. et al 1991).

Although the prime use of grinding aids is to reduce agglomeration of cement particles, their use will also assist in:

• The total or partial elimination of the ”coating” effect on the media,
• An improvement in the separator efficiency due to increased fluidity of fine particles,
• A decrease in pack-set problems in storage silos and bulk delivery trucks,

• An increased bulk and bag cement quality,
• Improved materials-handling (blowing into silos, off-loading trucks, etc.) due to an improved fluidity,
• Improved grinding production capacity.

The grinding aids application is more desirable, due to their significant effects on mechanical properties of cement, whose particle size distribution results narrower and shifted towards shorter diameters (Bathia, JS., 1979). The greater the surface of the hydraulically active components, the higher the Blaine fineness, the faster does the cement harden. Nevertheless, the Blaine value only gives an indication and not an absolute value, as it does not adequately reflect the fine fraction which is an important parameter for the grinding process and for the properties of the binder produced.

When cement clinker is ground using grinding aids a narrower particle size range is generated, as the percentage of very fine particles, which only influence the setting time, is reduced. This is why the strengths at equal Blaine values are higher than when grinding without grinding aids. With closed-circuit grinding plants it was also noted that cement ground with heavy circulating loads often contains smaller amounts of both ultra-fine and coarse particles. To some extent, the grinding aids force the mill to work with a higher circulating load (Magistri, M. and Presti, AL., 2007). Generally, the concentration range of grinding aids added is from 50 to 500 ppm. After the grinding process, the additives might not be any longer in their original chemical form. In addition, grinding aid composition might not consist of mixtures of pure compounds, but rather more complex raw materials (Jeknavorian, AA. et al, 1998).

I.3.1.1 Amines

Ethanolamines are used in several industrial applications such as: in the textile industry, in gas purification processes, as solubilizers for pesticides, as dispersing agents in the application of agricultural chemicals, as emulsifying agents, as catalysts in the production of polyurethanes and in the rubber industry. Also, it used as corrosion inhibitors, as pigment dispersants and as chemical intermediates for other chemicals products. Isopropanolamine in water is a medium strong base. Diethanolamine is classified as a hazardous air pollutant. Ethylene amines TETA and TEPA are used as asphalt additives, as corrosion inhibitors, as epoxy curing agents in the hydrocarbon purification, as surfactants, as dispersants, as chelating agents, as catalysts, as textile additives and fuel additives.
The commercial products of TETA and TEPA are often mixtures of alkanol amines and no single, pure compounds. TEPA is completely miscible in water and is not biodegradable. Hydroxyethyl-diethylenetriamine (HEDETA) is very soluble in water. Compounds relating to the class of amines merely modify particle size cement neutralized charges arising at rupture valence bond and catalyze hydration process to increase strength, both in initial and late periods of hardening. Glycol compositions mainly prevent agglomeration of cement particles in grinding process and exert little effect on change in particle size. The most effective influence on the processes of grinding and hardening have intensifiers based on surfactants (Shakhova; L.D. et al, 2014).

Triethanolamine (TEA)

Triethanolamine is used for various reasons in the cement industry. Depending on the amount of TEA it behaves differently in the cement production process. At an addition of 0.02% to Portland cement, TEA acts as a set accelerator, at 0.25% it acts as a mild set retarder, at 0.5% TEA acts as a severe retarder, and at 1% it is a very strong accelerator. The acetate of triethanolamine is also one type of grinding aid (Flatt, R.J. et al, 1998). The mechanism of the action of TEA in cement hydration is not completely understood. TEA is a weak base and in an aqueous phase, it is mostly in the molecular state. TEA has the ability to chelate with certain metallic ions such as Fe 3+ in highly alkaline media (Yilmaz et al, 1993).

In Portland cement pastes, TEA reduced the strength at all ages of hydration and setting characteristics were found to be drastically altered, especially at higher TEA contents. It is important to observe that, the use of TIPA is known to yield a reduction in setting times and significant increases in strength development at early and late ages, regardless of the cement type if it was compared with TEA (Perez et al., 2003; Sandberg and Doncaster, 2004).TEA could accelerate the reaction of C3A with calcium sulfate in Portland cement, but the addition of TEA will lead to a higher cement manufacturing cost and it seems not as effective as expected for the grinding production of blended cement, so the advantages of various grinding aids are needed to be considered in the cement grinding process (Yi Zang et al, 2016).

The evaluation of grinding aid (GA) effect on clinker processing in laboratory grinding mills is relatively simple. Yet, the results obtained cannot be directly transposed to industrial mills, given the fundamentally different operational modes and grinding parameters (Assaad; J.J., 2015). Grinding aids (GAs) are incorporated during clinker processing to reduce electrostatic forces and agglomeration of cement grains. Their chemical basis mostly includes ethanolamines such as triethanolamine (TEA) and tri isopropanol amine (TIPA) as well as glycols such as diethylene glycol (DEG) and propylene glycol (PG) (Teoreanu; I. and Guslicov; G., 1999) (Assaad; J.J., 2015).

The practical results of these additions (Gas) to the cement industry can be divided into two aspects including an increase in cement Blaine fineness and compressive strength for given specific energy consumption (Ec) and/or savings in electrical energy and Ec together with improved mill productivity for given fineness. The former direction is relevant when producing cement possessing increased fineness necessary for high early strength requirements (i.e., ASTM C150 Type III) (ASTMC150, 2012), while the latter is more and more demanded with today’s constraints regarding the reduction of usable energy (Assaad; J.J. et al, 2009).

Gartner, E., and Myers, D., 1993 observed increased iron solubility due to the chelating potential of TEA so more cement iron reacted to form mono and tri sulfates. Depending on the chemical composition of the Portland cement, TEA addition was observed to produce a gain in mortar strength in some cases. (Lee, C.Y et al, 2003) noted accelerated hydration of fly ash cement due to TEA addition but did not consider whether the hydration of Portland cement or fly ash is affected by TEA. Lee, C.Y et al, 2003 observed that overdosage of TEA leads to a decrease in strength. Because of its aluminum chelating potential, TEA was found by (Spencer, B.B., 2005) and (Palmer, D.A., 2003) to be able to extract aluminum phases from sludge. In analytic chemistry, complexometric titration is a standard procedure to quantify cations where unwanted Al and Fe ions are masked by the formation of stable complexes with TEA.