Both a hydraulic (wet) separation process and a dry separation process are used in combination to recover sand, bentonite clay and organics from foundry waste created during operation of a green sand foundry. These recovered ingredients are then recycled for reuse in making additional green sand molds.

Described is a process for the refinement of a quartz powder, comprising the step of separating microparticles of refractory minerals, in particular minerals containing rare earth metal compounds, from the quartz powder by an elutriation step.

In a known method for treating pourable, inorganic grain, a heated rotary tube is used that rotates about an axis of rotation and surrounds a treatment chamber that is divided into a plurality of treatment zones by means of separating elements. The grain is supplied to the treatment chamber at a grain inlet side and is transported, in a grain transport direction, to a grain outlet side and is exposed to a treatment gas in the process. In order, proceeding herefrom, to allow for reliable and reproducible thermal treatment of pourable inorganic grain, in particular SiO.sub.2 grain in the rotary kiln, in a manner having low and effective consumption of treatment gas, it is proposed for spent treatment gas to be suctioned out of a reaction zone of the treatment chamber, by a gas manifold that rotates about the longitudinal axis thereof.

One aspect relates to a process for the preparation of a quartz glass body, including providing a silicon dioxide granulate, wherein the silicon dioxide granulate was made from pyrogenic silicon dioxide powder and the silicon dioxide granulate has a BET surface area in a range from 20 to 40 m.sup.2/g, making a glass melt out of silicon dioxide granulate in an oven and making a quartz glass body out of at least part of the glass melt. The oven has at least a first and a further chamber connected to one another via a passage. The temperature in the first chamber is lower than the temperature in the further chambers. On aspect relates to a quartz glass body which is obtainable by this process. One aspect relates to a light guide, an illuminant and a formed body, which are each obtainable by further processing of the quartz glass body.

A method of washing and grading silica sand for glass production includes removing trash and relatively large contaminants from a sand feed material via a sequence of multiple vibrating screens, collection sumps, hydrocyclones, a density separator, a classification tank, and a dewatering screen. The resulting silica sand product is suitable for glass production.

A long term dust free mass of natural silica particles is produced by covering 10-60 percent of the total surface area of the particles with a thin film of white mineral oil with a low viscosity of less than 200 Saybolt SUS at 100 F. and preferably in the range of 60-100 Saybolt SUS at 100 F.

Described is a process for the refinement of a quartz powder, comprising the step of separating microparticles of refractory minerals, in particular minerals containing rare earth metal compounds, from the quartz powder by an elutriation step.

An apparatus for the wet attrition of particulate material comprising an attrition scrubber; a dewatering screen comprising a deck and a sump beneath the deck, the dewatering screen being mounted upstream of the attrition scrubber whereby oversize material from a downstream end of the deck of the dewatering screen passes into the attrition scrubber; and a hydrocyclone wherein an underflow, containing a coarser fraction of the feed slurry, passes out of a lower outlet of the hydrocylone while an overflow, containing a finer fraction of the feed slurry and most of the water, passes out of an outlet at the upper end of the hydrocyclone, a pump being provided for pumping material from the sump of the dewatering screen to the inlet of the hydrocyclone, wherein the underflow from the hydrocyclone is passed into the attrition scrubber.

A method for producing a low iron silica sand product suitable for glass production has an SiO.sub.2 content of at least 99.8% by weight, an Fe.sub.2O.sub.3 content of less than 0.008% by weight, an Al.sub.2O.sub.3 content of less than 0.1% by weight, and a CaO content of less than 0.05% by weight includes preparing a slurry of crude ore, wherein the crude ore has a sand content of about 75% to 80% by weight, a kaolin/mica content of about 15% to 25% by weight, a dark, heavy mineral content of about 1% by weight, and an Fe.sub.2O.sub.3 content of about 0.5% to 1.0% by weight. Particles having a size of less than about one hundred forty mesh are removed, and contaminant material is removed. The sand is then separated from the slurry, dried, and passed through a rare earth magnetic separator.

A method of washing and grading silica sand for glass production includes removing trash and relatively large contaminants from a sand feed material via a sequence of multiple vibrating screens, collection sumps, hydrocyclones, a density separator, a classification tank, and a dewatering screen. The resulting silica sand product is suitable for glass production.