Reuse of water purification sludge as raw material in cement production

The feasibility of partial replacement of siliceous raw material for cement production with water purification sludge (WPS) was investigated by X-ray diffraction, free-lime analysis, compressive strength testing and toxicity characteristics leaching procedure (TCLP). It is found that WPS has no negative effects on the consumption of free lime and the formation of clinker minerals. The samples with WPS from 4 to 10 wt.% have higher 3 days and 7 days strengths than the control. After 28 days, however, only WPS replacements <7% increased the strength of samples. It is noteworthy that heavy metals in WPS were almost completely incorporated into the clinkers, and up to 28 days the heavy metals were not detected in the leachates. From the above results of clinker minerals, compressive strength and leaching tests, it can be concluded that WPS has the potential to be utilized as an alternative raw material in cement production.     

Evaluation of blends bauxite-calcination-method red mud with other industrial wastes as a cementitious material: properties and hydration characteristics

Red mud is generated from alumina production, and its disposal is currently a worldwide problem. In China, large quantities of red mud derived from bauxite calcination method are being discharged annually, and its utilization has been an urgent topic. This experimental research was to evaluate the feasibility of blends red mud derived from bauxite calcination method with other industrial wastes for use as a cementitious material. The developed cementitious material containing 30% of the bauxite-calcination-method red mud possessed compressive strength properties at a level similar to normal Portland cement, in the range of 45.3-49.5 MPa. Best compressive strength values were demonstrated by the specimen RSFC2 containing 30% bauxite-calcination-method red mud, 21% blast-furnace slag, 10% fly ash, 30% clinker, 8% gypsum and 1% compound agent. The mechanical and physical properties confirm the usefulness of RSFC2. The hydration characteristics of RSFC2 were characterized by XRD, FTIR, (27)Al MAS-NMR and SEM. As predominant hydration products, ettringite and amorphous C-S-H gel are principally responsible for the strength development of RSFC2. Comparing with the traditional production for ordinary Portland cement, this green technology is easier to be implemented and energy saving. This paper provides a key solution to effectively utilize bauxite-calcination-method red mud.     

Utilization of flotation wastes of copper slag as raw material in cement production

Copper slag wastes, even if treated via processes such as flotation for metal recovery, still contain heavy metals with hazardous properties posing environmental risks for disposal. This study reports the potential use of flotation waste of a copper slag (FWCS) as iron source in the production of Portland cement clinker. The FWCS appears a suitable raw material as iron source containing >59% Fe(2)O(3) mainly in the form of fayalite (Fe(2)SiO(4)) and magnetite (Fe(3)O(4)). The clinker products obtained using the FWCS from the industrial scale trial operations over a 4-month period were characterised for the conformity of its chemical composition and the physico-mechanical performance of the resultant cement products was evaluated. The data collected for the clinker products produced using an iron ore, which is currently used as the cement raw material were also included for comparison. The results have shown that the chemical compositions of all the clinker products including those of FWCS are typical of a Portland cement clinker. The mechanical performance of the standard mortars prepared from the FWCS clinkers were found to be similar to those from the iron ore clinkers with the desired specifications for the industrial cements e.g. CEM I type cements. Furthermore, the leachability tests (TCLP and SPLP) have revealed that the mortar samples obtained from the FWCS clinkers present no environmental problems while the FWCS could act as the potential source of heavy metal contamination. These findings suggest that flotation wastes of copper slag (FWCS) can be readily utilised as cement raw material due to its availability in large quantities at low cost with the further significant benefits for waste management/environmental practices of the FWCS and the reduced production and processing costs for cement raw materials.     

Utilization of ferroalumina as raw material in the production of Ordinary Portland Cement

Red mud (RM), the digestion by-product of bauxite processing from “Aluminum Hellas”, was dewatered by means of a filter press. The filtrand with water content from 28 to 32 wt% was named ferroalumina (FA). In order to utilize it as a raw material in the production of Ordinary Portland Cement (OPC), mixtures were prepared with limestone, sandstone and 1, 3 and 5 wt% FA addition, respectively. The design of the mixtures was based on the cement's compositional indexes LSF, AM and SM. Burnability tests showed that less than 1 wt% free lime can be obtained in all cases for firing at 1450 °C, except for the mixture with 1 wt% FA addition, which requires 1550 °C. XRD analysis and optical microscopy examination showed that FA addition did not affect the mineralogical phases of the produced clinkers. The characterisation of the produced Portland cements indicated that differences on surface area, water requirement and setting time are negligible. Compressive strength results after 28 days of curing varies from 55 to 63 MPa, which ranks the produced cements in CEM I 42.5N category. More specifically, the cements with FA addition due to their relatively high 2-day strengths (>20 MPa) can be ranked in CEM I 52.5N category. Addition of FA increases the amount of water-soluble chromium proportionally to the amount of total chromium to the mixture; however, conversion of total Cr to hexavalent Cr remains practically constant, in the range of 32–35 wt%. The results indicate that FA can be used as raw material in the production of OPC up to 5 wt% according to the chemical composition of the other raw materials.     

Deficiencies of polypropylene in its use as a food-packaging material — a review

The outstanding chemical and physical qualities of polypropylene (PP) combined with an attractive price have made it one of the protagonists in the food-packaging industry. Like other polymers, however, PP tends to lose some of its constituents to the packed product, by migration, and when submitted to thermal, oxidative or radiation stresses PP starts to degrade. These processes are of concern when food is packed in the plastic, for they can cause PP to impart off-odour and off-taste to the packed product and in the worst case can give rise to toxicity of the food. This paper reviews the work that has been done on these processes and considers the recycling of PP for food-packaging use.