Phosphoric Acid Flocculation for Cadmium Precipitate Separation
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Solution Overview
Problem
The removal of heavy metals, particularly cadmium, from phosphoric acid containing compositions is challenging due to the very acidic and oxidizing conditions in the liquor, and the presence of calcium, which affects heavy metal precipitation, and there is a need for improved methods to meet stringent regulatory limits on heavy metal contamination.
Innovation Solution
A method involving the addition of a flocculating agent, such as a cationic or anionic polymer, to a phosphoric acid composition after the addition of a heavy metal precipitating agent, such as diorgano-dithiophosphinic acid, to promote the formation of agglomerates, facilitating the separation of heavy metal precipitates without the need for surfactants like sulfosuccinate compounds or polyethyleneglycol esters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional heavy metal removal methods are used in phosphoric acid digestion, then heavy metal precipitation occurs, but the separation efficiency is poor due to fine precipitate particles and the need for additional surfactants
Solution Approach 1:
The patent introduces a flocculating agent as an intermediary substance that mediates between the heavy metal precipitates and the phosphoric acid medium. This flocculating agent promotes the aggregation of fine precipitate particles into larger, easier-to-separate clumps, thereby improving separation efficiency without requiring additional surfactants or complex processing steps
Solution Approach 2:
The patent optimizes specific process parameters including pH control (maintaining pH 1.6-2.2 after 13-fold dilution), temperature (5-50°C), and the timing/amount of flocculating agent addition. These parameter changes create optimal conditions for both heavy metal precipitation and subsequent flocculation, transforming the separation process from inefficient to highly effective
2Manufacturing precision
If multiple chemicals including surfactants are used for heavy metal removal, then removal efficiency improves, but process complexity and cost increase
Solution Approach 1:
The patent combines the precipitation and flocculation functions into a single integrated process sequence. By adding the flocculating agent immediately after precipitation under controlled conditions, the method merges two separate chemical operations into one streamlined process, eliminating the need for separate surfactant addition and reducing overall process complexity
Solution Approach 2:
The flocculating agent serves multiple functions simultaneously: it facilitates precipitate aggregation, improves separation efficiency, and eliminates the need for additional surfactants. This multi-functional approach reduces the total number of chemicals required and simplifies the overall process while maintaining high heavy metal removal efficiency
3Ease of manufacture
If pH is not controlled during heavy metal precipitation, then the process is simpler, but precipitation efficiency decreases due to acidic conditions
Solution Approach 1:
The patent performs preliminary pH adjustment before adding the flocculating agent, ensuring the medium is optimized for precipitation. By controlling pH to 1.6-2.2 (after 13-fold dilution) in advance, the process creates optimal conditions for heavy metal precipitation, thereby improving precipitation efficiency without significantly complicating the overall process
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 method effectively removes heavy metals like cadmium from phosphoric acid compositions by forming stable agglomerates, allowing for efficient separation and reducing the need for hazardous by-products, while maintaining the purity of the final product.
Implementation Method 1
adding a flocculating agent, such as a cationic or anionic polymer, to a phosphoric acid composition after the addition of a heavy metal precipitating agent, such as diorgano-dithiophosphinic acid, to promote the formation of agglomerates
Implementation Method 2
precipitating the dissolved heavy metals by adding a heavy metal precipitating agent to the composition of step (a)
Data Source
AI summary
Improved methods for the removal of heavy metals, in particular cadmium, from an aqueous phosphoric acid containing composition, wherein an ionic polymeric flocculating agent is added to a phosphoric acid containing composition subsequent to the addition of an organothiophosphorous heavy metal precipitating agent to said composition, particularly under gentle mixing conditions, such as between 100 and 300 rpm. The flocculating agent promotes the formation of agglomerates of the heavy metal containing precipitate, thus facilitating their removal from the composition. More in particular, the phosphoric acid containing composition is obtained by the acid digestion of phosphate rock, preferably by nitric acid, sulfuric acid, or a combination thereof.