Refractory Grain Recycling via Chromium Reduction
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Solution Overview
Problem
Conventional processes for manufacturing sintered refractory products containing chromium(3) oxide face challenges such as high costs and difficulties in recycling used products due to the presence of hexavalent chromium, which is toxic and requires expensive and complex purification methods, often resulting in incomplete conversion to trivalent chromium and insufficient purity levels.
Innovation Solution
A process involving the milling of starting refractory products in a liquid medium to produce a suspension with particles less than 50 μm, followed by sintering and granulometric selection, which reduces hexavalent chromium content and achieves homogeneous sintered refractory grains with performance equivalent to those from new products, allowing for the recycling of both new and used materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional purification methods are used to remove hexavalent chromium from used refractory products, then chromium(6) levels are reduced, but the process becomes expensive and complex
Solution Approach 1:
The patent changes the oxidation state parameter of chromium from +6 to +3 through reduction treatment. By adjusting the chemical parameter (oxidation state) rather than removing chromium entirely, the process simplifies purification while ensuring safety through stable trivalent chromium formation that prevents re-oxidation during subsequent sintering.
Solution Approach 2:
The patent converts the harmful hexavalent chromium into beneficial trivalent chromium through reduction. The harmful substance (chromium(6)) is transformed into a harmless or beneficial form (chromium(3))) that provides refractory properties, thereby turning the waste problem into a resource recovery opportunity.
2Ease of manufacture
If used refractory products containing chromium(6) are recycled directly, then recycling cost is reduced, but the toxic chromium(6) content remains high
Solution Approach 1:
The patent applies preliminary reduction treatment to convert chromium(6) to chromium(3) before the sintering process. This preliminary action eliminates the toxic component in advance, allowing direct recycling of used refractory products without expensive post-processing purification steps.
Solution Approach 2:
The patent changes the chemical state of chromium from toxic hexavalent to harmless trivalent form through reduction. This parameter change enables safe recycling of used refractory materials by eliminating the toxicity barrier while maintaining material recoverability.
3Productivity
If conventional sintering is performed on mixed new and used refractory materials, then material utilization is improved, but chromium(6) may reform from chromium(3) during heating
Solution Approach 1:
The patent applies preliminary reduction to convert all chromium to the stable trivalent state before sintering. This preliminary anti-action prevents the unwanted re-oxidation of chromium(3) to chromium(6) during subsequent high-temperature processing, ensuring compositional stability throughout the sintering cycle.
Solution Approach 2:
The patent creates a reducing or inert atmosphere during sintering to prevent re-oxidation of chromium(3). By controlling the atmospheric environment (using reducing gases or inert atmospheres), the patent maintains chromium in the stable trivalent state throughout the heating process, preventing formation of toxic hexavalent chromium.
4Object-affected harmful factors
If filtration techniques are used to purify chromium-containing wastes, then chromium(6) is removed, but the process becomes time-consuming and expensive
Solution Approach 1:
The patent changes chromium from the harmful +6 oxidation state to the stable +3 state through reduction. This parameter change eliminates the need for time-consuming filtration and separation processes, as the reduced chromium(3) can be directly incorporated into the refractory product matrix without further purification.
Solution Approach 2:
The patent converts the harmful chromium(6) waste into beneficial chromium(3) material through reduction. This transformation eliminates the need for complex filtration and purification steps, turning a time-consuming waste treatment process into an efficient material recovery operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process effectively reduces hexavalent chromium levels, achieves high-purity sintered refractory products, and enables the recycling of chromium oxide-containing materials, improving the economic viability and safety of refractory product reuse while maintaining performance comparable to products made from new materials.
Implementation Method 1
milling of a charge to be milled comprising said optionally crushed starting refractory product, in a liquid medium in order to obtain a suspension of particles of said starting refractory product, more than 80% of said particles, as a mass percentage, having a size of less than 50 μm
Implementation Method 2
sintering of the green part to obtain a sintered body
Data Source
AI summary
A method for manufacturing sintered refractory grains containing Cr2CO3 from an initial refractory product including one or more chromium that includes: A) optionally, \crushing the starting refractory material; B) grinding a filler, comprising said starting refractory material in a liquid medium to obtain a suspension of particles of said starting refractory material; C) preparing a starting mixture including at least 1 wt % of particles of the suspension obtained during the preceding step; D) shaping the starting mixture into the shape of a preform; E) optionally drying the preform obtained in step D); F) sintering the preform so as to obtain a sintered body; G) optionally grinding the sintered body; and H) the optional selection by particle size.