Continuous Calcium Thiosulfate Production via CSTR Oxidation
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Solution Overview
Problem
Existing methods for producing calcium thiosulfate result in high solid byproducts and soluble contaminants, such as polythionates, which complicate the leaching of precious metals and reduce the effectiveness of the calcium thiosulfate as a plant nutrient.
Innovation Solution
A continuous process using multiple continuous stirred tank reactors (CSTRs) for the oxidation of calcium polysulfide with specific mole ratios of lime and sulfur under controlled temperatures and pressures, minimizing byproducts and polythionates, and employing acid treatment and flocculants for separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional batch processes are used for producing calcium thiosulfate, then production flexibility is maintained, but solid byproducts and soluble contaminants such as polythionates are generated in high amounts
Solution Approach 1:
The patent employs continuous stirred tank reactors (CSTRs) to replace batch processes, enabling continuous oxidation of calcium polysulfide to calcium thiosulfate. This continuous operation with controlled residence times and steady-state conditions minimizes the formation of solid byproducts and soluble contaminants like polythionates, achieving high purity product while maintaining production flexibility.
Solution Approach 2:
The patent optimizes critical parameters including oxygen partial pressure (0.5-2.0 atm), temperature (20-40°C), and residence time (0.5-4 hours) in the CSTR system. These parameter changes enable precise control over the oxidation reaction, maximizing calcium thiosulfate yield while minimizing unwanted byproducts and contaminants.
2Productivity
If oxidation reaction conditions are intensified to increase production rate, then productivity improves, but formation of polythionates and other contaminants increases
Solution Approach 1:
The continuous CSTR process maintains steady-state oxidation conditions with controlled oxygen supply and residence time, enabling high productivity without the formation of excessive polythionates. The continuous flow ensures consistent reaction conditions that prevent over-oxidation while maximizing production rate.
Solution Approach 2:
The patent implements monitoring and control of oxidation parameters including dissolved oxygen concentration, temperature, and pH to maintain optimal conditions. This feedback control prevents excessive oxidation that would lead to polythionate formation while sustaining high production rates of calcium thiosulfate.
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
This process produces high-purity calcium thiosulfate with minimal residual contamination, suitable for precious metal leaching and plant nutrition, reducing the need for further concentration and minimizing bacterial growth.
Implementation Method 1
the oxidation of calcium polysulfide with specific mole ratios of lime and sulfur under controlled temperatures and pressures
Data Source
AI summary
An efficient process for the continuous preparation of calcium thiosulfate (CaS2O3) from lime sulfur, through oxidation is described. The process involves oxidizing calcium polysulfide intermediate in a series of reactors to produce calcium thiosulfate as a clear liquid in high concentration with minimal byproducts. The process results in the complete destruction of polythionates, permitting the calcium thiosulfate produced to be useful in certain leaching processes for precious metals. The invention further makes it possible to recycle the process water from the leaching process for use as a raw material reactant in the process for calcium thiosulfate production.