Influence of P(V) on the characteristics of calcium silicates and the hydration of clinkers

Abstract

The effect of the addition of small amounts of meat and bone meal (MBM) ash on the clinkering process and on the hydraulic reactivity of obtained clinkers was studied. The study was aimed at simulating the clinker burning process in an industrial furnace that replaced up to 20 wt% conventional fuel with MBM used as alternative fuel. Laboratory clinkers were obtained by adding from 0 . 07 to 0 . 88 wt.% of MBM ash to an industrial raw mixture, and were compared with a clinker obtained without additions. The free lime content in the clinker increased steadily when the concentration of phosphorus was increased up to a level of 0 . 16 wt% P 2 O 5 in the raw mixture. With higher phosphorus additions the free lime content increased only insignificantly. The results of X-ray microanalysis indicated that a maximum of 2 . 3 and 3 . 3% of the silicon sites were replaced by phosphorus in alite and belite, respectively. The clinker containing 0 . 6 wt% P 2 O 5 slowed down the hydration process for approximately 1 day and thereafter began to exceed the degree of hydration of the reference sample. The values of degree of hydration of clinker rich in P 2 O 5 exceeded the reference sample at 7 and 28 days by approximately 3 and 5%, respectively. IntroductionThe industrial process of heating at high temperature in rotary kilns, which is essential in cement manufacture, creates favourable conditions for the use of waste materials as alternative fuels. Careful controls of plant operations, composition of the waste and emissions are necessary in order to ensure a good quality of cement product. Therefore, only certain types of waste can be considered as fossil substitute. The materials frequently used for this purpose are the following: meat and bone meal (MBM), solvents, used oils, waste tyres, sewage sludge, plastics, etc. 1-3 P 2 O 5 is present in clinker due to kiln feed as well as fuel ash compositions. It occurs in both primary raw materials (limestone and shale) as apatite in certain parts of the world 4,5 and in industrial by-products, which may be used as secondary raw materials (e.g. slags from the metal extractive industries). The partial replacement of fossil fuel by using MBM as an alternative represents a source of an additional amount of P 2 O 5: This is due to the ability of clinker to incorporate various levels of ash and the phosphorus inorganic compounds present in these materials would combine mainly with the silicates (alite and belite) formed during clinkering. 6,7 It has been shown that a high level of phosphorus inhibits the formation of alite. Halicz and Nathan 8 obtained synthetic clinkers that were prepared from oil shale containing up to 5 wt% P 2 O 5 as a secondary component. Although some clinkers contained more than 3 wt% P 2 O 5 , their mineralogical composition was satisfactory (50 to 60 wt% C 3 S). Gutt 6 showed that the limit of inclusion of phosphate ions in alite solid solution is about 1 . 1 wt% P 2 O 5 . High amounts of phosphate led to preferential formation of phosphatic dicalcium silicate so...

Meat and Bone Meal as a Renewable Energy Source in Cement Kilns: Investigation of Optimum Feeding Rate

“…Therefore, there must be other phenomena as well, along with above mentioned reason, which cause the 138% increase in free lime content at 7 t/hr MBM feeding. It has been shown [7], [23]- [27] that a high level of phosphorous stabilizes belite and hence inhibits the reaction between CaO and belite to form alite. Due to this reason the free lime content can be increased.…”

“…However, one study has been carried out to find out the effect of MBM ash addition on the clinkering process and hydraulic reactivity of clinker [7]. In another study [8] the air demand and energy input in the rotary kiln burner were investigated through an ASPEN PLUS model by partly replacing primary fuel by MBM.…”

On the phase chemistry of Portland cement clinker

“…Phosphorus has been shown to negatively influence the formation of alite and increases the amount of belite and CaO(s) formed. With increasing amounts of phosphorus pentoxide in the raw material of clinker, phosphorus was shown to primarily enter the belite phase and to a lesser extent the alite phase (Gutt, 1963;Nastac et al, 2007;Stanek and Sulovsky, 2009). At concentrations above 1% phosphorus pentoxide, a solid solution of phosphorus and belite forms (Nurse, 1952).…”

“…The use of wastederived fuels from agricultural crops, animal meat or bone meal, for example, leads to increased phosphorus content in cement. It has been shown that phosphorus decomposes or inhibits the formation of alite while stabilising belite and generating free lime (Halicz et al, 1984;Nastac et al, 2007;Nurse, 1952;Stanek and Sulovsky, 2009). The amount of alite in cement is of great importance because it is the most important contributor to the development of strength in concrete in the first 28 d. Because phosphorus is expected to increase when traditional fossil fuels are replaced with alternative biomass-based fuels, both theoretical and practical studies on how an increased phosphorous content influences clinker minerals have been performed.…”

Mathematical Model for Alternative Fuel Combustion in a Rotary Cement Kiln Burner

“…In another study, the flow of exhaust gases and the effect on operational parameters were found [8]. Furthermore, the effect of MBM ash addition on the clinkering process, a review of energy volarisation of MBM as well as environmental impacts of using MBM in cement kilns have been investigated [9]- [11].…”