Low-Temperature Reactive Crystallization for HCl Recovery
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Solution Overview
Problem
Conventional methods for recovering hydrochloric acid (HCl) from calcium chloride solutions, such as pyrohydrolysis, are not economically feasible due to high temperatures required, making it challenging to recycle HCl for industrial-scale HCl-based leaching processes, especially for calcium-based rock processing.
Innovation Solution
A continuous-stirred tank reactor process at temperatures below 70°C, where calcium chloride solutions are mixed with sulfuric acid and water to produce high-strength hydrochloric acid and calcium sulfate solid crystals, allowing for the recycling of HCl and processing of calcium-bearing ores.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pyrohydrolysis is used to recover HCl from CaCl2 solutions, then HCl can be recovered, but temperatures of up to 1000° C. are required making the process economically unfeasible
Solution Approach 1:
The patent changes the temperature parameter from 1000°C (pyrohydrolysis) to below 70°C (reactive crystallization), fundamentally altering the energy requirements. This is achieved by changing the chemical mechanism from thermal decomposition to low-temperature reactive crystallization using sulfuric acid, resolving the contradiction between HCl recovery reliability and energy consumption
Solution Approach 2:
The patent replaces the thermal/mechanical pyrohydrolysis system with a chemical reactive crystallization system. Instead of using high temperature to drive off HCl, the process uses chemical reaction between CaCl2 and H2SO4 to directly produce HCl at low temperatures, substituting one mechanism for another more efficient one
2Reliability
If conventional HCl recovery techniques are used, then HCl can be recovered, but the process is not economically feasible for CaCl2 solution treatment
Solution Approach 1:
The patent changes multiple parameters simultaneously: temperature (to below 70°C), reaction mechanism (to reactive crystallization), and product form (to solid calcium sulfate crystals). These parameter changes collectively transform an economically unfeasible process into a viable one by reducing energy costs and enabling continuous operation
Solution Approach 2:
The patent implements continuous reactive crystallization where CaCl2 solution, H2SO4, and water are continuously fed into the reactor, and HCl and calcium sulfate crystals are continuously produced. This continuous operation improves economic feasibility compared to batch processes, while maintaining reliable HCl recovery
3Reliability
If high temperature processing is used to recover HCl, then HCl can be recovered, but the process complexity and cost increase significantly
Solution Approach 1:
The patent replaces the complex high-temperature pyrohydrolysis system with a simpler low-temperature reactive crystallization system. The chemical reaction approach requires less complex equipment (no high-temperature furnaces, less sophisticated temperature control), reducing overall process complexity while maintaining HCl recovery capability
Solution Approach 2:
The patent introduces sulfuric acid as an intermediary substance that facilitates HCl recovery at low temperatures. The H2SO4 reacts with CaCl2 to directly produce HCl and calcium sulfate, serving as a chemical mediator that enables the transformation without requiring high temperature conditions
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 efficiently produces high-strength hydrochloric acid (up to 9.5 mol/L) and calcium sulfate crystals, enabling the recycling of HCl and reducing environmental impact by treating calcium chloride waste streams, thus making the metallurgical industry more environmentally friendly.
Implementation Method 1
converting the calcium chloride solution, sulfuric acid and water into HCl and calcium sulfate solid crystals
Implementation Method 2
producing calcium sulfate solid crystals and hydrochloric acid (HCl) from a calcium chloride solution
Data Source
AI summary
The present relates to a method for producing calcium sulfate solid crystals and hydrochloric acid (HCl) from a calcium chloride solution comprising the steps of feeding a continuous stirred-tank reactor with a calcium chloride solution, sulfuric acid and water; mixing the calcium chloride solution, sulfuric acid and water in the reactor; and maintaining the reactor a temperature of less than about 70° C., converting the calcium chloride solution, sulfuric acid and water into HCl and calcium sulfate solid crystals. The method described herein can be incorporated as a means for regenerating HCl from CaCl2 solutions which are generated in the metallurgical industry when processing calcium-bearing ores for recovering metals like rare earth elements.