Natural Iraqi palygorskite clay as low cost adsorbent for the treatment of dye containing industrial wastewater.

In this study, natural Iraqi low- cost locally available clay (palygorskite) was studied for its potential use as an adsorbent for removal Congo red from aqueous solutions. Batch type experiments were conducted to study the effect of contact time, initial pH of the dye solution, initial dye concentration, adsorbent dosage, and particle size of adsorbent on adsorption capacity of Congo red. The adsorption occurred very fast initially and attains equilibrium within 60 min. When the effect of pH of solution dye on the yield adsorption has been carried in a range of 2-10, the adsorption obtained was nearly the same with very slightly effect of pH and it was reported that above 49.07 mg/g of Cong red by palygorskite clay occurred in the pH range 2 to 10. It was observed that the removal of Congo red increase with increasing initial dye concentration and adsorbent dose, but, adsorption capacity decrease with increasing adsorbent dose. The adsorption capacity increase with decreasing particle size of adsorbent. The equilibrium adsorption data were interpreted using Langmuir and Freundlich isotherm models. The obtained results revealed that the equilibrium data closely followed both models, but the Langmuir isotherm fitted the data better. The maximum adsorption capacity was found to be 99 mg/g at ambient temperature. Results indicate that Iraqi palygorskite clay could be employed as a low cost alternative to commercial activated carbon in wastewater treatment for the removal of colour and dyes.

All-ceramic single-tooth restorations: choosing the material to match the preparation--preparing the tooth to match the material.

The shape of a crown preparation is the prime determinant for the choice of material for an all-ceramic restoration. One essential factor is the available space for the restoration, which requires a certain occlusal thickness. The dentist's preparation design determines the available vertical clearance, and the dental technician has the responsibility of advising the dentist with regard to either choosing the right material to match the preparation or to preparing the tooth to match the material. Assuming a minimum static fracture strength of > 2000 N, the following materials can be used for all-ceramic crowns: Laboratory surveys have shown that in most situations, the available occlusal clearance in clinical reality is only 0.8 to 0.9 mm (after cementing). This shows that the available space will often be insufficient for providing monoblock crowns and still on the tight side for veneered oxide ceramics (In Ceram, zirconia, etc.). However, crowns made of veneered oxide ceramics are much more complex to fabricate and much more expensive. By simply providing a minimal occlusal thickness of 1.5 mm, the treatment provider could therefore easily facilitate the use of the much more economical monoblock crowns without compromising either esthetics or strength. Actually, crowns with veneered oxide ceramic copings do not offer any higher fracture resistance compared to Mark II crowns as long as the minimum thickness requirements are met. The flexural strength of CAD/CAM-fabricated lithium disilicate rods is about twice that of CAD/CAM-fabricated Mark II rods. When used for crowns with a wall thickness of 1.5 mm, however, both materials exhibit the same fracture strength of between 2000 and 2500 N. This is related to the different reinforcing action of the adhesive luting agent, which is essentially required for both these materials. When choosing a material, preparation shapes, technical complexity and cost should be thoroughly compared and scrutinized and should figure prominently in the discussions between dentists and dental technician. Unfavorable preparation shapes for single crowns will necessitate compromises in terms of the choice of materials that result in high cost but do not offer anything in the way of higher fracture resistance. What constitutes an appropriate all-ceramic restoration for a single tooth? Do all-ceramic single crowns require the same material bulk as multi-unit bridges? Everything would indicate that a suitable preparation geometry allows feldspathic ceramic monoblock crowns to be milled that do not require any extensive finishing efforts such as thermal annealing or in-laboratory veneering while at the same time demanding no compromises in terms of esthetics and load-bearing capacity.